BOILING IN THE BRONZE AGEAuthor(s): Alan HawkesSource: Archaeology Ireland, Vol. 29, No. 3 (Autumn 2015), pp. 32-36Published by: Wordwell Ltd.Stable URL: http://www.jstor.org/stable/43631006Accessed: 11-07-2017 18:29 UTC

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Above: Pl. 1 - Reconstructed timber-lined trough during boiling

experiment at Rathbarry, Co. Cork (photo: author).

Right: Fig. 1 - The pyrolithic water-boiling process associated with

prehistoric burnt mounds in Ireland.

Articles Ireland unsurprising, on many burnt given times mounds the over dense have the distribution past appeared 25 of years. in the Archaeology site This type is Ireland many times over the past 25 years. This is unsurprising, given the dense distribution of the site type

across Ireland and the perceived ambiguous nature of the technology. Many discussions have focused on site function, a subject of debate and speculation since M.J. O'Kelly's excavations and experiments at Ballyvourney, Co. Cork, in the early 1950s. This contribution examines one aspect of site function, namely the apparatus used in the boiling process itself - the trough. A review of the existing burnt mound literature seems to indicate that all boiling troughs were of the same basic plan: rectangular and internally lined with wood or stone. This, however, is a false impression, as the surviving corpus shows considerable variation.

Boiling troughs associated with burnt mounds can be generally described as sunken pits, situated adjacent to hearths and often, but not always, internally lined. The method involved a process of heat transfer whereby water was boiled through the introduction of stones heated in a nearby fire (Fig. 1; Pl. 1). It has been proposed that troughs began to be internally lined sometime after 2000 BC.

32 Archaeology Ireland Autumn 2015

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Above left: Fig. 2 - Radiocarbon dates from sites with stone troughs in Ireland (Oxcal 4.12).

Above: PI. 2 - Excavated stone-lined trough and associated stone

working surface at Dromnea, Co. Cork (photo: Rose M. Cleary).

OxC a V42.4 Bfoni Rynsev 12»^). r.S . InC»" Ì almost*^ ay* I fawn y el » 20' v,

Macron îy Upper R_D ate(3354,21 ) - A-

Ballyna nona R_Date(3300,24) -

Castlecx)ke R_Date< *294,21) ^ļt

Brackbíiun R_Date(3í 76,35) - -

Ballyqu rk R_Date(32 '0,24) -4MI-

Clonmore North R_Déte( 31 97,34)

Scartbarry R_Date(31 70,90)

Leahys R_Date(3162,28) Ü*T 7

Garran« s R_Date(31 £ 2, 35)

Cahiracon R_Date(30 )0,80)

Ballydo wney R_Date( *090,60)

Clonmore North R_Díte(3090,60) -

Dromnta R_Date(3090,35)

Killoteré n R_Date(3070,70) -

Gortybr gane R_Date( 3053, 25) --

Cloonrreen R_Date(2í95,50)

Ballym< untain R_Datť (2992,35)

Coarha nore RJDate(: >950,80) -

Currina i R_Date(294l),50)

Bockagi R_Date(290D,25)

Lisnager R_Date( 2890,40)

Coolmo ohan R_Date( 2860,24)

Cuffsbo rough R Date [2780,35) -4*^.

Currina i R_Date( 2670,20)

Curragf Upper R_Date(2630, 24)

Ballinglunna North R_Date(2589,21 ^

Cashekluff R_Date(2e 40,25)

Brackbí iun R_Date(2f 00,34) A*ÁĚ&-:

Drombťg R_Date( 246 0,50)

Shannakea Beg R_D;te(2410,60) ** *■ ^ 3000 2500 2000 1500 1000 500 1calBC/1calAD

Calibrated date (calBC/calAD)

Recent excavations have confirmed that this practice occurred during the late Neolithic period (c. 2800-2500 BC). A trough typology was first proposed by John Ó Néill, who suggested that circular forms are

particularly early and rectangular forms are later in the sequence. While true for some sites, there are now simply too many exceptions in the archaeological record to make this a reliable dating application.

More likely is a development in relation to internal trough linings, where the evidence suggests that particular forms were favoured in different periods of prehistory.

Pit or boiling trough? Sometimes it can be difficult to establish whether some pits should be interpreted as troughs when there is no evidence of internal lining and where they are particularly shallow. The absence of some form of

visible lining in excavated troughs cannot be taken as proof that they

were unlined during use. During excavation, a trough is usually identified from other pits by a number of distinctive characteristics. These include evidence for internal lining, a roughly geometrical shape, steep sides and a flat base. Where a pit does not have any evidence for lining and the measurable volume is considerably less than lm3, the feature is generally interpreted as a non-boiling pit, although truncation by later activity on the site must be taken into

account. A study conducted by the author indicates that, between 1950 and 2010, 1,481 pit features out of a total of 3,271 (45%) from burnt mound locations have been interpreted as boiling troughs. Details relating to trough form suggest that almost half (48%) are

rectangular in plan, while oval forms account for 24% and circular forms 20%. The remainder are either irregular (3%) or square (1%), while 4% of troughs were not fully defined during excavation. It can

be difficult to distinguish between subrectangular, oval and subcircular troughs, as oval troughs can be of similar dimensions and

proportions to rectangular and subrectangular troughs but have rounded sides. It is possible, too, that many troughs have been altered through intensive use or later disturbance. The insertion of a timber lining may also have influenced the shape of a trough, as some timber-lined troughs are placed within larger irregular pits.

The function of trough linings The addition of a timber or stone lining allowed for more efficient water-boiling, maintaining the pit structure in wet ground conditions

and facilitating the regular clearance of heat-shattered stone from the

trough. It has been suggested that trough linings aided in water retention, but the use of wattle and roundwoods as lining materials would not have made pits watertight. The use of sphagnum moss as bedding layers under and between planks may have allowed the filtering of groundwater into the trough. The placement of some troughs over and adjacent to natural springs also seems to indicate a preference for fresh, clean water during trough use and suggests that there was some degree of planning in the siting of many pits. Seven different lining methods have been recorded in Ireland:

stone, planking, roundwood, wattle, clay, hollowed-out logs or a combination of these materials. Some 298 pits had stake-holes driven into the base and sides, suggesting the former presence of organic linings that no longer survive. A further 814 trough pits are recorded

as unlined, although the use of an organic lining may have been more common than the archaeological record suggests. Problems of poor preservation make it difficult to quantify the frequency of wood-

lined troughs. Their interpretation as troughs is generally based on their relative depths and whether the pit had straight sides and a flat base. Troughs may have intentionally been left unlined in dryer areas not prone to waterlogging, where the use of a stone or timber lining to minimise trough collapse was unnecessary. The excavation of troughs in areas where natural clays were solid and impervious may have been another reason why linings were not used. In these scenarios the troughs required manual filling from an adjacent water source.

Archaeology Ireland Autumn 2015 33

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Above left: PI. 3 - Excavated roundwood-lined trough with corner

supports at Bofeenaun, Lough Moore, Co. Mayo (photo: Conor McDermott).

Below: Fig. 3 - Radiocarbon dates from sites with roundwood-lined

troughs in Ireland (Oxcal 4.12).

Stone-lined troughs Stone-lined troughs are particularly uncommon when compared with examples found in the Scottish Isles. This may be related to the post-

abandonment history of sites, where deep ploughing disturbed or completely removed in situ stone slabs from the trough sides. It is possible that stones may have been removed for reuse elsewhere. The

scarcity of stone in certain areas may also have contributed to the minimal use of stone as a trough lining.

The remains of 57 stone-lined troughs have been recorded during scientific excavation since the mid-twentieth century in Ireland, with

average dimensions of 2.4m by 1.54m and depths of 0.49m (PL 2). Seventy per cent of these troughs are rectangular in plan, while the remainder are oval (16%), circular (10%) or square (4%). Four examples have associated paving slabs adjacent to the pit serving as kneelers, such as at Dromnea, Co. Cork. Frequently only the base of the stone-lined trough survives, owing to later truncation. Construction methods vary but most are built of large flat slabs that line the sides and base, with some evidence of deliberate shaping in order to fit the stones tightly together. While most stone troughs fill

naturally with water, clay used to seal the exposed joints has been noted in some. Stone lining is particularly common in rectangular forms, probably owing to difficulties in fitting slabs smoothly around

the curves of circular and oval examples. The use of stone lining was particularly prevalent during the middle to late Bronze Age, with 34 examples dated to 1500-500 BC. This dating evidence is derived from charcoal from mostly secure mound or trough deposits (Fig. 2).

Roundwood-lined troughs This form of lining has been identified in 37 troughs and is particularly common in rectangular forms. Of these, 28 rectangular/subrectangular troughs and nine circular or oval forms were lined with roundwood. The lining comprises a series of roundwood branches or brushwood tightly packed together along the sides and base of a trough and held in place by stakes in each of the corners (PL 3). Often a combination of different techniques was used

in certain parts of the trough, changing from rods to split roundwoods to planks. The most common wood species used in the construction of these troughs is a mixture of alder, ash and hazel, with occasional willow and oak. It is likely that roundwood was collected locally, with minimal working of this material for use as trough lining. Where preservation conditions are good, compressed moss is commonly found under the base and side timbers, acting as a filter for clean water. A total of 21 of the 37 examples were found to

contain moss bases, indicating that the structures filled naturally with

water. The identification of moss under and between these timbers

also suggests that roundwood troughs may only have been constructed in areas where they filled naturally with water, as the moss lining acted as a filter. This lining technique was common during the middle to late Bronze Age in Ireland (Fig. 3).

Wattle-lined troughs Wattle-lined troughs have become increasingly common in the Irish archaeological record, particularly as a result of infrastructural developments. They are quite distinctive and all conform to a basic set of characteristics - mostly circular (although some rectangular examples are known) and constructed with a series of upright stakes placed around the internal perimeter of the trough. These stakes are interwoven with horizontal sails. The linings are exclusively made of hazel or willow and are found only along the side walls of troughs, while the bases are lined with planks or flat stones (PL 4). There are, of course, exceptions, such as Killoteran 11, Co. Waterford, where the base was unlined, and Killoran 253, Co. Tipperary, where the base was

lined with transversely placed hazel rods. The use of wattle offers a more straightforward way of lining a

subrectangular, oval or circular trough and limits the amount of woodworking required. A review of the excavated evidence confirmed that pits with a high proportion of internal stake-holes around the perimeter are generally interpreted as evidence of a wattle lining that no longer survives. Thirty-four surviving wattle-lined structures have been uncovered in Ireland since the late 1990s, with

a further 31 possible examples. Of the surviving wattle elements, six have evidence of internal partitions or compartments, possibly used to separate cooked food from the fired debris. The identification of

34 Archaeology Ireland Autumn 2015

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Left: Fig. 4 - Radiocarbon dates from preserved wattle-lined troughs in Ireland (Oxcal 4.2).

Below: PI. 4 - Excavated wattle-lined trough with plank base at

Ballyclough North, Co. Wicklow (photo: Yvonne Whitty).

wattle linings in the archaeological record discounts previous suggestions that organic linings were used to make a pit watertight. The use of wattle to line a trough pit did not make a trough impermeable; rather the lining allowed water to seep into the trough. This interpretation is supported by the presence of sphagnum moss used as a filter in a number of examples, allowing clearer bog water to

fill the trough.

The evidence suggests that wattle-lined troughs are amongst the earliest types constructed for pyrolithic technology in Ireland and were particularly used during the Chalcolithic period, c. 2500-2000 BC (Fig. 4). Where wattle linings have survived intact, structural timbers from five troughs have been radiocarbon-dated to this period,

while thirteen have been dated by charcoal from associated fills.

Dugout canoes and hollowed-out tree trunks A number of troughs made from a single piece of wood may represent

reused log boats formed by hollowing out a large tree trunk. Seventeen examples have been found, thirteen recovered from excavation, of which six are from recent development-led projects. With the exception of alder troughs at Derrybrusk 1 and 2, Co. Fermanagh, all examples are of oak wood. The troughs usually survive

as single pieces of wood set into an elongated pit, often supported by stones along the sides. Where found, they are generally situated immediately adjacent to a formal hearth. Eleven of the troughs have been radiocarbon-dated from timber samples to 1900-800 BC. Three have been dated using dendrochronology to c. 1500 BC. Taphonomic processes might account for the low numbers of identified examples, as many of the larger elongated trough pits found at sites such as Ballyvourney II, Co. Cork, Barnkyle, Co. Limerick, and Rathduff 1, Co. Kilkenny, may originally have contained hollowed-out logs for water-boiling that have not survived.

Only two examples can be confirmed as canoes reused for pyrolithic water-boiling. A hollowed-out trough at Killalough, Co. Cork (PL 5), was formed by splitting an oak trunk longitudinally, then

hollowing out one half, which was the preferred method in log-boat construction. A groove noted at one end of the trough may have been used to attach ropes to the log boat to allow more efficient

manoeuvrability during transportation. At Curraghtrasna, Co. Tipperary, the trunk was split down its length in two places to form the base and two sides. End beams consisting of unworked tree trunks

were then pegged into position at the long ends. Victor Buckley identified this trough as a reused canoe or log boat.

Plank-lined troughs The use of planks is the most common method of trough lining in prehistoric Ireland, with 145 examples (PL 6). In many cases, dressed timber planks demonstrate the competent craftsmanship involved in this form of trough construction and imply an experienced community of woodworkers familiar with what was required, working to a well-understood plan.

Plank-built troughs generally survive in the archaeological record

as either partially lined pits (usually base planks) or as whole timber structures where anaerobic conditions allow for preservation. These linings are most commonly found in rectangular troughs, of which there are 105 examples with average dimensions of 2.1m (L) by 1.3m (W) by 0.4m (D). Of these, 48 examples have accompanying stakes/stake-holes or pegs used to support the sides and possibly to help fasten the base planks together. While planks often line the base of wattle-lined troughs, it is unlikely that the sides of any circular or

oval pits were often lined with planks owing to the difficulties in fitting planks smoothly around the curves of circular and oval troughs. Nevertheless, a review of the excavation record has identified twelve circular/subcircular and seventeen oval types where plank lining was used. Some ovoid forms may, however, originally have been rectangular structures set into differently shaped pits. Alternatively, modern truncation of the pit walls may have altered the

shape of the pits, while wattle walls in some may have been removed, leaving only the base planks in situ. Post-use disturbance may have resulted in an over-representation of the number of circular and oval

pits lined only with planks, although a small number can be interpreted as circular plank-lined troughs.

Excavation has demonstrated that base planks were usually inserted first, followed by the side walls and supporting stakes. In the

majority of cases the base planks are laid parallel with the side timbers, as opposed to being laid transversely in the pit. In rare cases,

grooves can be found in the base planks to facilitate the placement and tight fit of the side planks. Others have more complex timber constructions, such as the mortised plank box troughs at Killoran, Co.

Tipperary, and Ratheen, Co. Limerick. Plank linings are usually oak (29%), alder (14%) or ash (7%), and can sometimes be constructed using a number of different species. Most trough timbers, however,

Prim ¡3?^). 'k wyý ff p

Gortarne R_Date(4080,30; -

Deerpc rk East R_Date(38: 10,40)

Killoteran R_Date(3820,35)

Hughe itown R_Date(3783,56) ' ****<

Cionco wan R_Date(3710,(i0)

Kilbegl *y R_Date(3653,26|

Sonnai jh R_Date(3645.40

Ba I rea ik R_Date( 3643.30 ^

Heaths town R_Date(3620 40) -

Leacarow R_Date(3620,32) ~ ^

Correagh R_Date(36 13,25)

CoolacDrk R_Date(3599,4 I) - *

Banda R_Date(3549, 32)

Ballina^r R_Date(3483.40)

Lisdorr an R_Date(3460,80)

Caraur More R_Date(323 1, 64) - - -

3500 3000 2500 2000 1 500

Calibrated date (calBC)

Archaeology Ireland Autumn 2015 35

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Left: Pl. 5 - Log boat/canoe reused as a water-boiling trough at Killalough, Co. Cork (photo: Eamonn Cotter).

Below left: Fig. 5 - Proposed trough development in Ireland.

Below: PI. 6 - Late Bronze Age plank-lined trough at Cahiracon, Co.

Clare (photo: Emer Dennehy).

cannot be identified to species (43%) owing to the degraded condition of the remains. Radiocarbon dating has demonstrated that plank linings are common throughout the prehistoric period, with examples dating from the late Neolithic to the early Iron Age.

Conclusions- observations on trough form While this paper has focused on internal linings, other related trough features identified in recent years, such as overflow outlets, emptying

pits and drains and water-inlet channels, highlight the multifaceted design of burnt mounds. Such features highlight a degree of

sophistication in the siting and construction of troughs and are design components that add a further complexity to these boiling receptacles.

While many troughs retained the basic rectangular form, the internal structure is not confined to planking alone. The archaeological record now indicates considerable variation in trough design. Trough shape does not show a chronological sequence, and radiocarbon dating has shown that specific trough shapes are not restricted to particular periods but are spread across the entire date range for burnt mounds. It is likely that other functional and social factors determined their form, with larger troughs possibly used for a

greater output of food during periods of feasting or for bathing activities. There does, however, appear to be a development in relation to internal trough linings (Fig. 5). Wattle-lined troughs are on

present evidence a Chalcolithic/early Bronze Age tradition, whereas stone-lined pits and hollowed-out forms are more common during the middle to late Bronze Age. Plank linings, on the other hand, were

prevalent throughout the Bronze Age, with the earliest examples found in late Neolithic contexts. ■

Further reading Hawkes, A. 2014 The beginnings and evolution of the fulacht fia

tradition in early prehistoric Ireland. Proceedings of the Royal Irish

Academy 114C, 89-139. Hawkes, A. 2015 Fulachtaí fia and Bronze Age cooking in Ireland:

reappraising the evidence. Proceedings of the Royal Irish Academy 115C, 1-51.

Ó Néill, J. 2009 Burnt mounds in northern and western Europe: a study

of prehistoric technology and society. VDM Verlag, Germany.

36 Archaeology Ireland Autumn 2015

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