SPECIAL ISSUE

Shelters over the Megalithic Temples of Malta:debate, design and implementation

J. Cassar • M. Galea • R. Grima • K. Stroud •

A. Torpiano

Received: 11 May 2010 / Accepted: 23 August 2010 / Published online: 9 September 2010

� Springer-Verlag 2010

Abstract The Maltese Megalithic Temples, constructed

between the mid-fourth and mid-third millennia BC, are

unique and are amongst the oldest stone buildings of such

complexity in the world. They are of great local and

international significance, embodying symbolic, educa-

tional and recreational values. These Temples are currently

suffering from a series of severe problems associated with

the deterioration of materials as well as structural prob-

lems, seen in a number of serious collapses in recent years.

In 2000, it was decided that these vulnerable prehistoric

structures needed to be protected from the direct impact of

environmental factors by means of a temporary, open-sided

shelter, conceived as a large parasol designed to be as light

as possible, in visual as well as in physical terms. The

erection of two of these shelters took place during

2008–2009. The performance of the shelters is currently

being assessed by environmental monitoring which already

indicates an improvement in conditions beneath the shel-

ters when compared to conditions on site before sheltering.

Keywords Malta � Megalithic Temples � Shelters �Environmental monitoring � Conservation

Introduction

The Maltese archipelago lies in the central Mediterranean

Sea, some 90 km south of Sicily. The Islands are rather dry

with limited woodland, although they offered the basic

resources, such as soils, water and building materials,

which were necessary for the first human inhabitants to

settle around the start of the fifth millennium BC.

The archipelago is entirely made up of sedimentary

rocks, the geology comprising a layered structure of Lower

Coralline Limestone at the bottom, above which is Globi-

gerina Limestone, then Blue Clay, with the topmost For-

mation being the Upper Coralline Limestone. Globigerina

and Coralline Limestone are the main building materials

available on the Islands and have been used since the very

first buildings appeared.

The Maltese Megalithic Temples

Following the first human settlement, the prehistoric

landscape soon changed with the appearance of impressive

monumental structures. These structures, known today as

the Maltese Megalithic Temples, were constructed between

the mid-fourth and mid-third millennia BC. They are

unique and are amongst the oldest stone buildings of such

complexity in the world. Nothing remotely like these

Temples has been discovered outside the Maltese Islands.

They represent a distinctive architectural form that was

highly innovative and sophisticated for its time, making

them a fundamental reference point for the history of

architecture.

The value of these prehistoric sites has been recognised

by the United Nations Educational, Scientific and Cultural

Organization (UNESCO). The _Ggantija Temples, on the

Electronic supplementary material The online version of thisarticle (doi:10.1007/s12665-010-0735-8) contains supplementarymaterial, which is available to authorized users.

J. Cassar (&) � A. Torpiano

Faculty for the Built Environment,

University of Malta, Msida MSD 2080, Malta

e-mail: joann.cassar@um.edu.mt

M. Galea � R. Grima � K. Stroud

Heritage Malta, Triq il-Missjoni Taljana,

Kalkara KKR 9030, Malta

123

Environ Earth Sci (2011) 63:1849–1860

DOI 10.1007/s12665-010-0735-8

smaller island of Gozo, were inscribed on the UNESCO

World Heritage List in 1980, and in 1992 this inscription

was extended to include the other Temple sites of Ha _gar

Qim (Fig. 1), Mnajdra, Skorba, ta’ Ha _grat and Tarxien. In

nominating these monuments for inclusion on the World

Heritage List, the Government of Malta has committed

itself to safeguard these sites on behalf of the international

community.

Today, the Megalithic Temples have a great signifi-

cance. Their unique nature has made them synonymous

with the Maltese Islands, turning them into a powerful

symbol of Maltese national identity. In addition, their

exceptional character has also made them a key component

in the promotion of the Maltese Islands as a distinctive

holiday destination, directly contributing to tourism which

is one of the pillars of Maltese economy.

These Temples also have considerable educational as

well as recreational values. With one of the highest pop-

ulation densities in the world, Malta has very limited

availability of open spaces for recreation. However, the

presence of these prehistoric sites has contributed to the

preservation of large open spaces that are today invaluable

for recreation purposes. Being also an educational resource

of great potential, they are utilised to illustrate the

achievements of the Temple Culture, the transition from

the Neolithic to the Bronze Age, the prehistoric origins of

human exploitation of the Maltese archipelago, the

changing relationship between people and their environ-

ment, and the problems of sustainability and resource

conflict in a small island context.

It is therefore not only for their captivating qualities and

their significance in understanding prehistoric societies, but

also for their value to society today that considerable

investment in time and money has recently been made in

the preservation of the Megalithic Temples.

Materials and structure

Both Globigerina Limestone and Coralline Limestone,

widely available in outcrop in the Maltese Islands, have

been used in the construction of the Megalithic Temples.

Globigerina Limestone, by far the most commonly used

material, forms part of the Oligo-Miocene ‘‘soft lime-

stones’’ widely found in the Mediterranean basin, including

Turkey, Israel, Tunisia, Spain and Italy. This Formation is

made up of three Members, the Lower, Middle and Upper

Globigerina Limestone, with the Lower Globigerina

Limestone being used as the main local building material.

It can be described as a pure limestone (calcite [92%),

containing small amounts of quartz, feldspars, apatite,

glauconite and clay minerals. Its porosity is very high,

reaching values of up to 40% (Cassar 2002). Freshly

quarried Globigerina Limestone is pale yellow in colour,

and is fine-grained and generally homogeneous in texture.

Sections where bioturbation is concentrated also occur, and

in other areas concentrations of yellow or brown stains can

be found. Besides this stone type, both the Upper and the

Lower Coralline Limestones can be found used in the

Temples. These two limestone Formations are composed of

different strata that vary widely in appearance and strength.

The type of rock outcropping on the surface did not

influence the choice of location for the building of a

Temple structure (Grima 2004). The Temples are in fact

built mainly of the stone type available in the immediate

vicinity. For example, the outer wall of the Mnajdra

Temples is built of Lower Coralline Limestone, a stone

type abundantly present in the immediate vicinity. Globi-

gerina Limestone, on the other hand, was brought in from

nearby, and was used for the internal walls and decorative

elements. The Temple of Ha _gar Qim, on the other hand, is

built entirely of Globigerina Limestone as no Coralline

Limestone is readily available nearby.

The mode of construction is megalithic, with stones up

to 6.40 m long being used to build a series of adjacent

curved apses, apparently without the use of any bedding

mortar. Built over a period of a thousand years, the Tem-

ples, however, have a number of consistent characteristics.

These include the use of free-standing megaliths which

form ‘‘trilithon’’ portals along the main axis of the Tem-

ples, whilst other uprights were used to build semi-circular

apses, arranged along the axis, with horizontal megaliths

laid in ‘‘courses’’ above (Torpiano 2004). The facade is

normally concave and is composed of upright stone slabs,

known as orthostats. Above the orthostats, the wall is

continued upwards in horizontal blocks. Surviving hori-

zontal courses, as well as contemporary depictions of the

Temples, suggest that these buildings were originally

roofed. The roof was constructed in corbelled masonry

courses, possibly capped by a flat roof. All the Temples

Fig. 1 The facade of the main building at Ha _gar Qim, before

sheltering (Photo taken by M. Galea)

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consist of an outer and an inner wall, with an infill of earth

and stone.

Ha _gar Qim and Mnajdra

The prehistoric Temples of Ha _gar Qim and Mnajdra are

found in a garigue landscape along the south-western coast

of Malta. Standing at the top of a ridge, with the ground

sloping away on all sides, Ha _gar Qim must have always

been a conspicuous landmark. Mnajdra Temples, visible

from Ha _gar Qim, are found 500 m downhill, above the

southern cliffs.

The complex of Ha _gar Qim consists of one large

building and two smaller separate structures. The main

building appears to have been created in a succession of

interventions during the fourth millennium BC, resulting in

an unusually irregular and complex ground plan.

Mnajdra consists of three main buildings (Fig. 2). The

earliest of the three is the small East Temple, built around the

mid-fourth millennium BC. A particular characteristic of

Mnajdra is the orientation of the South Temple. This building

is aligned with the rising position of the sun during the

Equinox and Solstices, suggesting that the prehistoric soci-

ety that built it observed the motion of the stars, the moon and

sun, probably relating them to the changing seasons and

times of planting and harvesting crops.

Discovery

The remains of Ha _gar Qim were never completely buried

after they fell into disuse. They were first mentioned in

print in 1647 (Abela 1647) and were also depicted in an

engraving in the 1780s (Houel 1787). This engraving and

accompanying description clearly show that while the

majority of the site was buried, the top parts of the taller

megaliths remained visible. The curiosity elicited by the

visible megaliths is what probably led to the early exca-

vation of the site, in 1839, followed by that of Mnajdra in

1840 (Vance 1842).

Supplementary excavations at Ha _gar Qim were carried

out in 1885. At the time, the sites were believed to be

Phoenician, but in 1910, further excavations at the sites

confirmed their prehistoric origins (Zammit 1927). In 1954,

a number of trenches were excavated within these two

sites, with the objective of ascertaining the relative chro-

nology of the various parts of the Temples (Evans 1971).

This further confirmed the prehistoric origins of the sites,

but it was only through the application of carbon dating

techniques to the Maltese prehistoric sequence in the 1960s

that the Temples of Ha _gar Qim and Mnajdra were

unequivocally attributed to the fourth millennium BC.

Deterioration of materials and structural problems

All the Megalithic Temples of Malta are currently suf-

fering, to a greater or lesser extent, from a series of

problems, including those associated with the deteriora-

tion of materials as well as structural problems, mani-

fested dramatically in a number of serious collapses

which have occurred with increasing frequency in recent

years. Concern on the state of conservation of these sites

is however long-standing (Davey and Plenderleith 1965).

Studies were commenced in the 1980s to understand the

precise state of conservation of the Temples, the nature

and extent of their deterioration, as well as to identify the

causes of the damage observed (Cassar et al. 1989;

Vannucci et al. 1994; Tampone et al. 1994). These

studies, extended over the years and culminating in a

Conservation Plan for the Megalithic Temples (2008),

have shown that the main forms of deterioration of this

softer stone within the Temples include powdering, flak-

ing and scaling of the stone surface, as well as alveolar

weathering leading to advanced forms of back-weathering

(Fig. 3). These manifestations, together with the frequent

presence of efflorescence on the surface of the megaliths,

have led to the conclusion that salt crystallisation is the

main cause of deterioration of this material (Cassar 2002).

A general model for the deterioration of this stone has

been established over the years (Vannucci et al. 1994;

Fitzner et al. 1996; Rothert et al. 2007), and corresponds

closely to the various deterioration processes occurring on

the prehistoric megaliths. These manifestations and their

intensity vary because of local differences in salt content

and types, which are mostly, but not exclusively, of

marine origin (Torfs et al. 1996), and also because of the

differing quality and weathering resistance of the stone

(Cassar 2002).Fig. 2 Aerial view of Mnajdra Temples, before sheltering (Photo

taken by D. Cilia)

Environ Earth Sci (2011) 63:1849–1860 1851

123

In addition, the Temples are also suffering from struc-

tural damage, manifest as fissured or broken megaliths, and

apparent also through the rotation and occasional collapse

of individual megaliths, sections of walls or even entire

apses (Conservation Plan for the Megalithic Temples

2008). Apart from the fact that the weakened material does

at times lead to the partial or complete collapse of sections

of these Temples, it has also been recognised that the

washing out of the soil that constitutes much of the fill of

the double walls of the structures leads to individual

architectural elements, as well as the structures as a whole,

being considerably weakened, making them more prone to

collapse, particularly during heavy rains (The Megalithic

Temples of Malta World Heritage Site Management Plan

2008). Human action, ranging from vandalism to miscon-

ceived ‘‘restoration’’ works carried out in the past, has also

taken its toll on these sites.

Conservation concerns and interventions over time

Ever since the first excavations took place at Ha _gar Qim

and Mnajdra, conservation and restoration work has been

carried out with the aim of addressing these problems.

However, the first restoration works were particularly

aimed at a better understanding of what the monuments

may have originally looked like; ‘‘…some of these

imposing works of Maltese Cyclopean art might be made,

with a little skilful restoration, to look almost as complete

as when they were originally constructed’’ (Caruana 1886).

Attempts at achieving this were made by reinstating

megaliths to their presumed original positions and where nec-

essary, supporting them with modern walls or pillars. A

lithograph published in 1842 depicts stone pillars built in small

ashlar blocks supporting broken horizontal slabs. The rein-

statement of megaliths also included those lying on the ground

in front of the facade of Ha _gar Qim, placed in their presumed

original positions as part of the horizontal coursework of

the facade. Numerous similar interventions also took place

in the South and Central Temples at Mnajdra.

In trying to restore the original appearance of the

Temples, and at times also to try to regain lost stability,

broken megaliths were repaired using what is presumed to

be Portland cement. Such repairs were made at these sites

as early as 1910, and in a few examples at Ha _gar Qim,

these repairs were accompanied by the insertion of metal,

usually iron, dowels to hold the broken parts of the

megalith together (Cassar 1988). In 1949, areas of the

remains where it was estimated that the extent of disinte-

gration was so advanced that the adjacent and overlying

structures were in imminent danger of collapse, the blocks

were ‘‘restored’’ by covering the deteriorated blocks in

cement mixed with Globigerina Limestone chippings

(Evans 1971). This treatment was intended to improve the

appearance of the remains and to protect the megaliths

from further deterioration. Curators were oblivious to the

deleterious effect that cement has on the stone and were in

fact acting in accordance with international standards at a

time when the Athens Charter for the Restoration of His-

toric Monuments (1931)1 approved the use of concrete for

the consolidation of ancient monuments.

In other interventions, a better understanding of the original

architecture of these monuments was attempted through the

reconstruction of sections of missing walls in dry-stone

walling. The earliest example of this type of reconstruction

occurred at Ha _gar Qim in 1885. In 1910, the same technique

was used on the facade of the Central Temple at Mnajdra;

similar works also took place during 1953–1955 (Ashby

et al. 1913; Stroud 2007). These reconstructions are still

clearly visible on site, and while providing an effective

representation of the original architecture of the monu-

ment, they can easily be identified as a recent intervention.

They also were, and are, reversible.

In more recent years, catastrophic incidents such as

collapses seem to have increased in frequency and in

intensity, requiring a number of extensive interventions to

take place, also to preserve the still standing walls adjacent

to the areas of damage. The most serious collapse in recent

times occurred in April 1994, when part of the wall sepa-

rating the Central Temple from the South Temple at

Mnajdra collapsed following heavy rains. Extensive works

to restore and consolidate the area of collapse were

undertaken (Torpiano 1995) and completed by 1996

(Stroud 2007). Although this intervention was by nature

Fig. 3 Alveolar weathering and back-weathering in an apse at Ha _gar

Qim. The progressive loss of material from the megaliths has now

compromised the structural stability of the chamber walls (Photo

taken by J. Cassar)

1 http://www.icomos.org/athens_charter.html.

1852 Environ Earth Sci (2011) 63:1849–1860

123

reactive to the collapse, some preventive measures were

also taken at the time to limit the possibility of a recur-

rence. A new wall was constructed in concrete bricks

behind the original megalithic wall so as to retain the soil

and stone infill and to prevent it from exerting pressure on

the original wall. In addition, a rainwater drainage system

was installed in the Central Temple.

Another collapse, this time at Ha _gar Qim, occurred in

November 1998 when a stretch of megalithic masonry

forming the wall between two apses collapsed. Part of the

restoration of this wall, which took place in 2001, involved

the introduction of a pillar constructed in well-squared

Globigerina Limestone blocks to replace one of the

megaliths which had completely disintegrated and was

unable to support the overlying structure.

In 2001, a shocking vandal attack took place in four

apses at Mnajdra. During this incident a large number of

megaliths were dislodged from their original positions. The

restoration of the damaged megaliths carried out in the

following months involved the return of the dislodged

megaliths to their original locations as well as the repair of

damage (breakage) they sustained during the attack. Other

minor collapses have also occurred more recently, each

requiring a targeted intervention to reinstate the displaced

megaliths.

Although concern had been voiced as early as 1910 on

the ‘‘disintegration’’ of some of the megaliths, few attempts

were made to preserve the actual material fabric of the

Temples, probably due to the lack of suitable materials and

techniques. The first, and probably most suitable, attempts

consisted in moving some of the decorated blocks indoors

for better preservation (Mayr 1908). There were also var-

ious endeavours to apply ‘‘stone preservatives’’ to a num-

ber of blocks with the intention of preserving them or

slowing their rate of deterioration (Ashby et al. 1913).

More recently, and until the mid-1970s, linseed oil in

kerosene was applied every summer to the limestone

megaliths (Cassar 1988).

However, it was gradually realised that reactive mea-

sures aimed at reversing damage in specific areas were

inadequate to address the problem. It was also necessary to

have detailed information on the causes of deterioration.

Monitoring

In 1999, following an international meeting of experts held

in Malta to identify the way forward for the conservation of

the Megalithic Temples, a Scientific Committee was set up

specifically to look into the problems of deterioration of the

Temples and to recommend solutions. At an early stage,

this Committee consisting of archaeologists, scientists,

architects and engineers, established that present-day risks

to the sites are mainly due to environmental factors directly

impinging on the structures and their materials. Informa-

tion gathered through previous studies was collated and

analysed, in order to determine which factors could inform

a better understanding of the current state of the Temples

(Stroud 2007). In addition, in order to understand the

impact of the surrounding environment on the already

weakened materials, a comprehensive, long-term and

continuous environmental monitoring campaign was laun-

ched in 2005 by Heritage Malta, which commissioned the

Italian CNR-ISAC2 to carry out a 1-year monitoring pro-

ject, following which monitoring has been continued by

Heritage Malta. Apart from measuring environmental fac-

tors, such as rain, wind speed and direction, air temperature

and relative humidity, solar radiation, and air pressure, that

were already being monitored at Ha _gar Qim by a weather

station obtained in 2000 through UNESCO funding, this

intensive 1-year campaign also included monitoring of

vibrations, water runoff, soil moisture, air pollutants, bio-

logical aerosols and surface temperatures including thermal

imaging (Fig. 4), as well as surface mapping of biological

crusts, localised wind field surveys inside the Temples, and

chemical analyses of the stone and deterioration products.

In this way, a clear picture of the current state of conser-

vation of the Ha _gar Qim and Mnajdra Temples, as well as

detailed information on the surrounding environment,

could be obtained.

External conditions: the environment

The studies of the immediate environment surrounding the

Temples needed to be placed in the context of what was

already known about the Maltese climate in general, to be

able to understand general but also local effects on the

structures. Being typically Mediterranean, with mild wet

winters and hot dry summers, the Islands have a total

annual average rainfall of only 600 mm that falls between

October and March with occasional storms and rather

heavy downpours that may even happen in August and

September. Winds are known to be fairly strong and fre-

quent and can peak at Force 11 in severe storms. There are

hardly any days without any wind. The prevailing wind is

north-westerly, while the other directional winds hail from

a north-easterly direction and tend to bring stormy weather;

the other major winds hail from the south-east and tend to

persist in early spring and autumn, bringing hot humid

wind and Sahara dust from North Africa. The relative

humidity is nearly always high and rarely falls below 40%.

2 Consiglio Nazionale delle Ricerche, Istituto di Scienze dell’At-

mosfera e del Clima (CNR-ISAC) (National Research Council,

Institute for Atmospheric Sciences and Cilmate).

Environ Earth Sci (2011) 63:1849–1860 1853

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Temperatures do not usually go below 2.6�C in winter

although temperatures below 0�C have been registered at

grass height level.3 In summer, temperature in the shade

can go beyond 39�C. The days of sunshine are quite high in

number and vary between seasons, but the number of hours

per day in any day varies according to cloud cover. The

number of sunshine hours peaks in July at 12.5 h, while the

smallest number of sunshine hours, in December, normally

amount to around 5.20 h.

Local conditions

The data collected at the Temple sites showed that

whereas, as expected, the local conditions generally

reflected what was occurring in the wider context of the

Maltese Islands, there were also typically localised phe-

nomena which needed to be understood. This included the

prevailing winds in the area, where wind direction was

found to vary, but was predominantly south-westerly to

north-westerly at Ha _gar Qim and north-westerly to north-

easterly at Mnajdra. It was found that the Temple sites

were nearly always windy, with speeds reaching Force 8

not being uncommon; the maximum speed ever recorded

was at Mnajdra at 28.85 m/s (Force 11) on 4 March 2009 at

21:45 from a north-west by west direction. The air tem-

perature varies from 2.6 to around 39.3�C,4 whereas the

relative humidity varies from 12 to 99.90%, rarely falling

below 30% and occasionally approaching 100% in Sep-

tember. On a typical sunny day, the global radiation load is

divided as follows: 9% ultra-violet radiation, 45% visible

light radiation and 46% infra-red radiation. Global radia-

tion was found to have particularly high values; mean

annual solar radiation load on 1 m2 of horizontal surface is

typically in the range of 5 kW/day (6 kW in summer, 4 kW

in winter).5 The maximum stone surface temperature ever

recorded was in May 2006 when 45�C was measured on a

west-facing megalith at Ha _gar Qim. The minimum

stone surface temperature recorded was in February 2006

with a value of -0.4�C from an easterly orientation at

Ha _gar Qim.

These environmental data collected over time proved to

be crucial in the study of deterioration mechanisms

occurring within the megaliths, and also allowed for the

identification of possible solutions for the conservation of

the Temples, at least in the short term.

Damage caused by environmental factors

Research has confirmed that the main instigator of

material damage is the presence of soluble salts, in

particular chlorides acting on a very porous and weak-

ened stone. One could therefore evaluate which of the

measured environmental factors could play a role in

material damage, and how it could do so. The high

values of solar radiation recorded, as well as the high

surface temperatures recorded on the megaliths, could be

related to the state of conservation of the various apses,

where it was found that megaliths in full exposure to the

Fig. 4 Infra-red thermal images showing the rapid thermal gain that

occurs in the space of a few hours in megaliths exposed to direct

insolation. The top image shows a group of megaliths on 29 June

2005 at 11.30 am; the bottom image shows the same megaliths 4 h

later at 3.30 pm [Images taken by Istituto di Scienze dell’Atmosfera e

del Clima (ISAC)]

3 The lowest temperature ever recorded at that height (grass height

level) was -3.6�C (3.6�C below freezing) on 17 March 1982

(Meteorological Office Newsletter 2009).

4 Data Statistics from Preventive Conservation Unit (Heritage Malta

2008).5 Data collected by CNR-ISAC.

1854 Environ Earth Sci (2011) 63:1849–1860

123

sun were often found to be in bad condition, whereas

stones which are never in direct sunlight were in better

condition (Fig. 5). It is well known that stone surface

heating leads to thermoclastic weathering and also

influences biological growth. Weathering is also affected

by the mostly high, but fluctuating, air relative humidity

registered; this brings about salt movement in the stones,

and can lead to salt crystallisation—efflorescence and

subflorescence—with ensuing damage. The registered

persistent and often high winds play an important role

not only in the aggravation of wetting and drying cycles,

but also transport sea salt aerosol, dust and other pol-

lutants and deposit them on the megaliths, and also cause

mechanical damage in the form of abrasion/erosion due

to soil/dust impact. The monitoring programme has

established that when the ground is saturated by 10 mm

of rain, water runs off, carrying with it top soil and

small stones particularly following the first rains in

autumn, quantifying the suspected impact of rainfall on

the terrain for the first time. The most significant vari-

ation in topsoil erosion was in fact found to occur in

October due to the intensity of the first autumn rains and

the lack of vegetation following hot and dry summer

conditions. Contrary to expectations, in winter erosion

was found to be less intense as vegetation cover provides

considerable protection.

The shelters: why shelter?

In 2000, an extraordinary meeting of the Scientific Com-

mittee was convened to define short-term recommenda-

tions for the protection of the Temples. A long debate

ensued recapitulating what was known at the time on the

causes of deterioration and possible ways of mitigating

these. It was concluded that a short-term solution was

needed to alleviate these effects. Whereas it was recogni-

sed that the knowledge available at the time would not

permit the safe application of methods of direct interven-

tion on the Temples, it was concluded that short-term,

preventive, indirect intervention would not only help pre-

serve the Temples from the most serious effects of

weathering, but would also be reversible, and thus, ‘‘buy

time’’ until ongoing research could possibly help by iden-

tifying safe methods of acting directly on the stones and the

structures. The Committee members unanimously agreed

that the direct impact of environmental factors on the

unprotected and weakened structures needed to be

mitigated.

It was thus decided to propose to the Maltese Govern-

ment that a temporary, open-sided shelter would be erected

over the most vulnerable Temple sites.

The shelters would mitigate the effects of: solar radia-

tion by directly shading the Temples, greatly reducing

thermoclastic weathering; eliminate the effects of water

through rainfall; mitigate against water runoff and prevent

the leaching of infills which could impart structural insta-

bility; reduce herbaceous growth; and mitigate wind

impact.

It was, however, also recognised that it was still unclear

at the time how air temperature and relative humidity could

change under the shelter (still being monitored), how the

wind speed could impact the stone, through sea salt aerosol

and dust deposition (still being studied), and how wind

turbulence would be affected (still being studied/moni-

tored). Hence, the start of the environmental monitoring

campaign described above.

The recommendations of the Scientific Committee were

presented to Cabinet in August 2000 and this resulted in a

go-ahead for what proved to be a long process of design

and implementation of the proposed shelters over the sites

of Ha _gar Qim and Mnajdra.

Fig. 5 Two views of apses at Mnajdra showing different extents of

weathering. Weathering processes are invariably more evident in

areas more exposed to solar radiation (Photo taken by J. Cassar)

Environ Earth Sci (2011) 63:1849–1860 1855

123

Design of the shelters: requirements

As the protective shelters are meant to protect these fragile

structures from the main agents of deterioration, and in

order to ensure that the existing hygrothermal balance

within the materials was not drastically modified by the

intervention, it was clearly important that the protective

shelters should not create a complete enclosure for the

Temples—even if this meant that it would be difficult to

reduce the damaging effects of wind. On the other hand,

reducing the amount of rainwater which falls directly on

the Temple should also have the effect of reducing the

deleterious effects of wind currents drying out the stone

surfaces. In effect, the recurring salt crystallisation cycles

would be diminished, thus reducing also the associated

damage.

The protective shelters were therefore conceived as a

large parasol. The design brief required that the chosen

structure be lightweight, in visual impact as well as in

physical terms, that the structure be capable of covering the

irregular shape of the Temples that needed covering, and

that, whilst it shaded the Temple stones, it also allowed

light to enter in sufficient quantities to avoid casting a

black patch of shade over them. At the same time, it was

also necessary that the protective shelters be capable of

erection, and eventually also dismantling, without hazard

to the Temples. They also had to be reversible, with as little

impact on the ground as possible. Overall cost, and ease

and cost of maintenance were obviously also important

considerations.

Another important requirement was that any possible

relationship between the orientation of the axes of both

Ha _gar Qim and Mnajdra Temples and celestial bodies

would not be obscured by the protective shelters. In both

Temples, there are sight lines that link views of the Tem-

ples with each other, and with the nearby small island of

Filfla; at Mnajdra, as already mentioned, there are impor-

tant links with the rising position of the sun at summer and

winter solstices and the equinoxes. It was also important

that the structure should not inhibit the reading of the fore-

court at Mnajdra as part of the Temple structure, and that

the fore-court should not be obstructed by any footings or

similar.

The actual design

It was thus essential that the design of the structure ensures

that such relationships are maintained. The original pro-

posal was for a single latticed arch to support a Teflon-

coated membrane, anchored at various points around the

Temple, with the location of footings, or anchor-points,

selected by ensuring that all of the above criteria were

fulfilled. The profile of the latticed arch was designed so

that adequate clearance would be achieved above the

highest of the Temple megaliths (a height of 4.5 m).

During the process of approval of this proposal, however,

major objections were raised about the overall height of the

arch, and the visual impact such a structure would have on

the area. The proposal was subsequently amended to one

involving a pair of latticed or trussed arches, meeting at the

same foundation points, thus achieving a lower overall

height (Fig. 6).

The trussed arches are the main supporting structures of

each shelter. These have a triangular cross-sectional con-

figuration, with a 324-mm diameter steel tube at the top

vertex of this triangular cross-section, while two 194-mm

diameter steel tubes form the lower vertices. The span of

the arches varies from 53 m at Ha _gar Qim, to 67 m at

Mnajdra. The shape of the membrane cover depends

exclusively on the geometry of the supporting arches and

the tensile stresses which are induced in the membrane by a

number of peripheral cables anchoring it to the ground. The

membrane form, and the subsequent fabric patterning, was

determined by a computerised form-finding process. The

form derived was then tested using wind-tunnel modelling,

in order to determine the forces generated in the arches,

and especially in the arch foundations and cable anchor-

points. Various scenarios, including accidental failure of a

number of cables in high winds, creating asymmetrical

loading conditions, were modelled in order to obtain the

worst case design loadings for the foundations.

The archaeological importance of the site imposed a

number of limitations on the design of both the foundations

of the arches and the membrane anchorage points. A

detailed debate on the type of foundations that would be

allowed was engaged in with the Superintendence of

Fig. 6 A temporary tower-frame was erected to support the shelter

arches during their installation over Mnajdra (Photo taken by J.

Cassar)

1856 Environ Earth Sci (2011) 63:1849–1860

123

Cultural Heritage, which had overall responsibility to

ensure that intervention was minimal, and that no damage

was done to the site. In order to avoid any excavations or

drilling into the ground, one option was to adopt heavy

concrete blocks, heavy enough, i.e., to resist the upward

forces generated at the cable anchors, and the horizontal

forces acting at both cable anchors and arch foundations.

However, the relative calculations showed that the size of

each concrete foundation block required would be in

excess of 30 m3, implying that the visual impact of such

foundations would be very significant. The alternative

approach was to make use of inclined ground anchors, for

the cable foundations, and concrete pad foundations sta-

bilised against horizontal forces by a limited number of

reinforced concrete piles. The process of designing such

foundations was very demanding since it was necessary,

first of all, to ensure that the geotechnical engineering

interventions would be as limited as possible, and would

not create any archaeological deficit, whilst ensuring an

appropriate level of safety, even in the case of extreme

storm conditions. Rigorous design reviews and a number of

re-designs were required to ensure that these conditions

were met.

When the final form of the arches and the membrane had

been determined, the resulting positions of foundations and

anchor points were marked on the respective sites, in order

to verify any possible archaeological implications. An

archaeological investigation was carried out at each point,

with the active participation of the Superintendence of

Cultural Heritage. Drilling was permitted only when the

Superintendence was satisfied that no archaeological assets

would be affected. In those cases where archaeologically

sensitive situations were discovered, the designers were

required to modify the position of the foundation or anchor

point, in order to mitigate the archaeological impact. This

was not an easy task since the form of the membrane cover

and the supporting arches could only be maintained by the

resultants of tension forces acting in the same direction of

the resultants of the cable/strut system that had already

been proposed. This meant that the options for any alter-

native tension cable configurations and anchor points were

severely limited. It was not possible to move a particular

anchor point outwards, along the existing line of action,

without some means of deflecting the relative cable from

its current direction, and this would invariably imply some

attachment to the ground at practically the same location as

the current cable anchor. The alternative approach was to

replace the cable by two, symmetrically arranged on either

of its sides, in order to maintain the forces in balance.

In the case of the arch foundations, the displacement of

the point where horizontal forces are taken into the ground,

via a drilled pile, was theoretically possible, using a pair of

horizontal compression struts symmetrically arranged on

either side of such line. This, however, implied that the

number of anchor piles drilled into the ground would also

increase—it possibly could even double. It was important

to emphasise that even if the drilling points of the piles,

required to absorb the horizontal forces, were shifted hor-

izontally, the contact point between the ends of the arch

and the ground would remain unchanged, and the transfer

of vertical load would need to occur at the same point. This

meant that this contact point would still need to be covered

by the arch foundation. The process of archaeological

assessment, proposing mitigation measures, re-designing of

foundation anchorage detail, and obtaining the relative

approvals, proved to be a difficult one, especially since, by

this time, the fabrication of the membrane, and of the

supporting arches, had already started, and could not be

easily modified. In some instances, this required the fab-

rication of very particular steel extensions to the proposed

foundations.

The final design issue was the selection of the membrane

fabric. The most important characteristics for such material

were its durability, particularly under UV exposure con-

ditions, temperature and humidity variations and salt spray,

and the light transmittance that could be achieved. Other

important characteristics included the tensile strength, the

dimensional stability, and, obviously, the cost. PTFE6-

coated (Teflon) glass cloth was selected for the membrane

material, giving a life of 20–25 years. PTFE is one of the

most inert plastic materials available and does not depend

on UV absorbers, pigments and flame-retardant additives to

improve its performance. It is also self-cleaning, and, in the

sun, it bleaches to a brilliant white colour.

The environmental performance of the protective shelter

is, obviously, an important consideration. The main pro-

tective features of the shelter are its ability to shield the

Temple structures from direct rainfall, particularly the high

intensity rain storms that have, repeatedly, caused col-

lapses, and the ability to shade the Temple structures from

the sun. The requirement of shading had to be balanced

against the requirement of allowing sufficient light trans-

mission to prevent a dark black shadow on the site. Tests

carried out in laboratory conditions have shown that this

type of fabric decreases the thermal fluctuations of the

surface of the megaliths by at least 5�C, or more depending

on the amount of light transmittance.

Implementation

Although detailed plans and method statements for the

implementation process had been required and submitted at

tendering stage, and in greater detail at planning

6 Polytetrafluoroethylene (PTFE).

Environ Earth Sci (2011) 63:1849–1860 1857

123

permission stage, the actual implementation of the shelters

on the ground presented a fresh series of challenges, not all

of which were predicted or expected. Some of them, as

already explained, centred on the great archaeological

sensitivity of the site. Other instances, where details of the

proposed processes and equipment needed to be refined,

included measures to take into account the changing

weather conditions. Throughout this process, very frequent

site briefings, discussions and updates between the con-

tractors, engineers and site curators were vital. Close

communication between all the parties was essential to

overcome the obstacles presented by their different per-

spectives, professional formations and technical languages.

As a result, curators were aware of the technical difficulties

being encountered at every stage of implementation, and

conversely, were able to ensure that the solutions adopted

were the most sensitive possible to the fragility of the site

and its setting. An essential ingredient in this communi-

cation was that the site curators maintained a constant first-

hand presence on site throughout every moment of the

implementation process.

The implementation of the shelters may be divided into

four principal stages, corresponding to the different com-

ponents of the cover. The first was the construction of the

foundation system required to anchor the shelters to the

ground. The second was the construction of the supporting

steel arches, two at Ha _gar Qim and two at Mnajdra (Fig. 7).

The third step was the installation of the series of cables

forming the flexible framework holding the membrane

panels in place. During the fourth and final stage, the 18

membrane panels forming each of the two shelters were

unfurled, stretched, and welded in place. Each stage pre-

sented different issues and challenges.

One of the first practical problems encountered during

implementation has already been mentioned: that during

the archaeological excavations of the areas which were to

act as anchor points, the discovery of archaeologically

sensitive situations required a modification of the position

of the foundation or anchor point, in order to mitigate the

archaeological impact. Once the cores for micro-pile

anchors started to be drilled, other problems arose in that

those that had a very low inclination from the horizontal

could only be drilled after further excavation of the sur-

rounding topsoil had been conducted, and a different piler

brought on site.

Another issue that had to be resolved at piling stage was

the preservation of as much as possible of the toprock

surface around the area of the piles that were to be drilled.

A fundamental characteristic of the shelters is that they are

entirely reversible, except where their foundations cut into

bedrock. In order to help mitigate the impact of the foun-

dations, it was considered desirable to preserve where

possible the toprock in these piles, with the long-term goal

of reinstating this rock in situ if the shelters were ever to be

dismantled in the future. In the case of Mnajdra, the

extreme hardness of the Coralline Limestone did not permit

the preservation of the rock core with the equipment

available. In the case of Ha _gar Qim, however, the softer

Globigerina Limestone permitted the lifting out of the core

from three of the four 900 mm piles required for the arch

foundations.

The site protection measures which had been planned at

design stage were also the subject of much discussion and

revision. A key concern was the protection of the ground

around the megalithic structures while the large piler was

manoeuvred into position. The original intention was to lay

a sand bed over plastic sheeting to form a track all along

the access route for the piler. In practice, a simpler, more

flexible and more effective method was adopted. This

consisted in laying rubber tyres on the ground for the steel

tracks of the piler to run over while avoiding any sharp

turns, which tend to disturb the ground surface.

The greatest surprises that were encountered during

implementation were to be the ones caused by the ele-

ments. Delays during the revision and implementation of

the foundations led to much of the shelter assembly work

taking place over the winter months, while at an earlier

stage it had been hoped that these would have been con-

cluded before the end of summer. The winter of

2008–2009, during which much of the work was realised,

turned out to be one of the harshest in recent years. Heavy

rains slowed down the works and resulted in waterlogged

soils which required more precautions to be taken when

manoeuvring cranes and heavy vehicles over them. Fero-

cious winds took contractor and consultants by surprise not

once but twice. Early on the morning of 23 January 2009,

Force 6 winds with Force 7 gusts split apart the first

membrane panel that had been installed over Mnajdra a

Fig. 7 The completed membrane shelter over Qim, Ha _gar viewed

from the south, showing arch supports and tension cables (Photo

taken by A. Torpiano)

1858 Environ Earth Sci (2011) 63:1849–1860

123

few days earlier. The panel that was damaged was still in

the process of being stretched into place to take its final

form, a process that was taking longer because of the low

winter temperature, which prolonged the process of creep

necessary for the PTFE membrane material to stretch and

set into its final shape. After assessing the damage, con-

tractor and consultants were quick to provide reassurances

that the failure of this panel was in no way to be taken as an

indicator of the performance of the completed shelter. A

panel that had not yet been tautened into shape was much

more vulnerable to damage. In order to reduce the risk of a

reoccurrence, a web of straps was installed on either side of

each fresh panel as it was being installed to help prevent it

from being blown out of position. Using this new system,

the installation of the remaining panels at Mnajdra and the

replacement panel for the damaged one went on apace.

Nature had one more surprise in store however. On the

evening of Wednesday 4 March 2009, gale force winds hit

the Islands. Weather forecasts till that same morning had

not predicted a gale. One of the very last membrane panels

that was to form a part of the shelter over Mnajdra was in

fact opened and raised into place that very morning.

Shortly after 2130, wind velocities of over 28.6 m/s were

recorded by the weather station at Mnajdra. In spite of the

additional protective measures that had been taken after the

first incident, this panel was torn in two. However, despite

these setbacks, the two shelters were successfully com-

pleted by the end of June 2009 (Fig. 8).

Conclusions

The preliminary results of the environmental monitoring

during the first year since the completion of the shelters

have registered dramatic reductions in temperature

variation and in wetting-and-drying cycles, as well as a

general drop in wind velocities in the sheltered areas. In

June 2010, bird-nesting was observed for the first time in

the shelter over Ha _gar Qim. Ornithologists have advised

that the simplest deterrent method is suspending short

lengths of aluminium foil in affected areas. At the time of

writing (July 2010) preparations are underway to have

these installed. The only undesirable side effect of the more

stable conditions below the shelters is the appearance of

some endolithic plants in some areas of Mnajdra, which are

being closely monitored in case they become cause for

concern and require treatment.

Encouraged by these very positive preliminary results,

the conservators, scientists and curators responsible for the

site have now begun to evaluate whether the goals of the

conservation strategy embarked upon in 2000 are being

achieved. Even as the shelters begin to slow down the

attrition rate suffered by the monuments, direct work to

consolidate the structures themselves is gathering

momentum as is the research on the panoply of purposely

designed conservation solutions required to address the

material and structural problems faced on these sites. The

long-term goal of this work is to make the preservation of

these monuments less reliant on the shelters in the future.

At present, however, the prospect of removing the shelters

appears remote.

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