Analysis of three private hydraulic systems operated in Apamea during the Byzantine period

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Analysis of three private hydraulic systems operated in Apameaduring the Byzantine period

Michaël Vannesse a, Benoit Haut b,*, Frédéric Debaste b, Didier Viviers c

aDépartement d’Histoire, Université de la Martinique, BP 7207 Campus de Schœlcher, 97275 Schœlcher, Martiniqueb TIPs, Université Libre de Bruxelles, Avenue F.D. Roosevelt 50, C.P. 165/67, 1050 Bruxelles, BelgiumcCReA-Patrimoine, Université Libre de Bruxelles, Avenue F.D. Roosevelt 50, C.P. 175/01, 1050 Bruxelles, Belgium

a r t i c l e i n f o

Article history:Received 10 December 2013Received in revised form18 March 2014Accepted 22 March 2014Available online 1 April 2014

Keywords:AqueductApameaCisternNymphaeumWater

a b s t r a c t

In this paper, three hydraulic systems (two nymphaea and a private bath), excavated in three houseslocated in the southeast of the city of Apamea and operated during the Byzantine period, are describedfrom an archaeological point of view and using fluid mechanics. Information (mostly unpublished) aboutthe architecture of these systems, their construction material, their construction date and their operation(water flow rate .) is provided.

The cisterns of these three hydraulic systems were previously understood as being dedicated to collectrainwater. It is clear today that these cisterns belonged to larger systems and that they were not meant tosimply collect rainwater.

There was probably no precise period for building these hydraulic systems. They spread gradually viamajor projects scattered over time, as they belong to the embellishment of the Apamean houses duringthe Byzantine period.

The similarities and differences between these systems are discussed. This comparison highlights theprobable existence of Roman good practice rules in the construction of nymphaea.

The analysis of the data presented in this work stresses highly probable evidence about connectionsbetween an operative aqueduct and the hydraulic systems analyzed in this work. These are valuableresults, as no documented information about water adduction is available for the southern half of the cityof Apamea, except for a distribution table.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The archaeological site of Apamea in Syria, on the right bank ofthe Orontes, between modern Hama and Aleppo, has a humanactivity that can be traced back to the Middle Palaeolithic. After theconquest of Alexander the Great, a Greek city was established therein 300/299 BC by Seleucus Nicator, the King of Syria. Apameabecame one of the main cities of the Seleucid Empire.

Later on, Pompey attached Apamea to the Roman territories (64BC). Because of several violent earthquakes, especially in the sec-ond, fourth and sixth centuries AD, the city saw large re-constructions that benefitted from liberalities of Roman andByzantine Emperors.

As the capital of the province of Syria Secunda, Apamea reachedgenuine prosperity during the fifth and sixth centuries AD, in theByzantine period. The Persian Wars combined with dramatic

earthquakes subsequently weakened the city and made it vulner-able to the Arabic conquest in 638 AD.

Since the beginning of the second century AD, a large street withporticoes (Cardo Maximus, see Fig. 1) offered to the city a monu-mental artery by which the town was intersected from north tosouth (Balty, 1988). The only known water supply of the city is anaqueduct, used from 47 AD (Balty, 2000). It was bringing water intothe town from a spring located about 80 km away from Apamea(Balty, 1987; Vannesse, 2011). This aqueduct entered into the townat its northeast corner.

The archaeological excavations in Apamea are coordinated bythe Archaeological research center (CReA) of the Université Libre deBruxelles (ULB). Some of the excavations areas are presented inFig. 1. Unfortunately, the site has been under heavy bombing inearly 2012, during the seizure of the nearby city by the Syrian Army.Subsequently, the site has been massively plundered throughillegal diggings.

Romans had a remarkable knowledge of the engineering ofwater supply (Hodge, 2008; Mays, 2010; Ortloff, 2009; Viollet,

* Corresponding author. Tel.: þ32 26502918.E-mail address: [email protected] (B. Haut).

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Journal of Archaeological Science 46 (2014) 245e254


2004). They used water for the irrigation of cultivated fields andfor urban needs. According to Vitruvius, water not only satisfiesthe needs of the people, but also their pleasure (Morgan, 1960).In the cities, fountains flourished; large baths and latrines wereoperated. During the Byzantine period, a decline in the quality

of the water systems is commonly admitted. In many cities, likeConstantinople, it is thought that the aqueducts were aban-doned and that the Romans focused on the construction ofcisterns, often very large, intended to collect rainwater (Viollet,2004).

Fig. 1. Archaeological excavations in Apamea.

M. Vannesse et al. / Journal of Archaeological Science 46 (2014) 245e254246


Only a few Roman writings on their water engineering tech-niques have been preserved. However, archaeology offers someprecise illustrations of these techniques. This is especially true inthe Middle East, where numerous Romanwater supply systems arevery well preserved. The surviving written records of Vitruvius(Morgan,1960) and Frontinus (Evans, 1994; Herschel, 1973) providesome understanding of water supply systems in the Roman period.While these works give insight into the construction methodologyof water supply systems of that period, they reflect pre-scientificviews of fluid mechanics principles (Ortloff, 2003). For instance,in the work of Frontinus, such a concept as the flow rate is notknown.

As a modern resource, fluid mechanics provides researchers andarcheologists with a tool to analyze the engineering details of theRoman water supply systems. Fluid mechanics principles enablethe simulation of the flow of water through archaeological remainswith a good level of conservation, opening new possibilities for theanalysis of these ancient water systems (Chanson, 2001; Haut andViviers, 2007; Ortloff and Crouch, 2001; Ortloff, 2003).

Due to the political and administrative status of Apamea, it canbe assumed that the water engineering practice in Apamea is anexcellent picture of the most advanced Roman technology in LateAntiquity. Consequently, the analysis of the remains excavated inApamea in order to highlight the organization of the water supplysystem of the city has been, during the last decade, an importantelement of the researches led by the CReA in Apamea.

For instance, a large bath complex (approximately 1200 m2)has been excavated between 2003 and 2010 in the north of thecity, to the east of the Cardo Maximus (see Fig. 1). This bathcomplex has been operated from the second to the seventh cen-tury AD (Paridaens and Vannesse, in press). Nearby excavations inthe northeast area of the city (see Fig. 1), where the aqueduct goesinto the town, were realized between 2002 and 2005. Theyrevealed at least four main periods of (re)construction, charac-terized by different water systems (Viviers and Vokaer, 2007;Viviers, 2008). The fourth and most recent of these water sys-tems was built at the end of the fifth century AD. In this system,water was carried inside the city limit in a masonry channel (an“inner aqueduct”), parallel to the Cardo Maximus (see Fig. 1). Fromthis masonry channel, several branches (terracotta pipelines witha pressure driven flow) were organized, for instance to fill cis-terns. An analysis of this fourth water system, using fluid me-chanics principles, has been realized. A water flow rate of 500 l/sin the inner aqueduct has been computed, from the aqueductinner slope measurement and from the evidence of wall sinterdeposits on the inner canal lining. It has been evaluated that theflow in this inner aqueduct was subcritical (i.e. Froude number< 1,high water level and low velocity). This analysis has alsodemonstrated that the branches had been designed based on anexcellent technical knowledge of water supply (Haut and Viviers,2007).

It is important to notice that these excavations demonstrate thatthe Byzantine city was not only using the aqueduct built in theRoman period, but was also able to rebuild a new water supplysystem, including an inner aqueduct (Vannesse, 2011; Viviers,2008). These results are in contradiction with what was previ-ously mentioned about Apamea by Balty (1987), who thought thatthe Byzantine city, since the sixth century AD, was no longer fed inwater by an aqueduct and that the numerous cisterns constructedduring the Byzantine period, for instance in the southern part of thecity, were dedicated to collect rainwater.

The inner aqueduct is elevated on pillars to give it sufficientheight to ensure water delivery. Remains of the inner aqueductwere excavated only in the northern part of the city (see Fig. 1). Thefull covered canal is preserved only for approximately 20 m, but

numerous pillars have been excavated. The slope of the full coveredcanal has been measured equal to 2.1 mm/m (Haut and Viviers,2007). The slope of the Cardo Maximus is almost constant andequal to 5 mm/m. It means that, during each kilometer of its courseinside the city, the inner aqueduct rose approximately 3 m abovethe ground level. This result has been confirmed by measurementsof pillar heights.

There is a lack of documented information about water adduc-tion in the southern part of the city, in the Byzantine period. Theonly excavated remains (found in 1938 and now lost) attesting for awater adduction during Byzantine times in the southern part of thecity is a water tower (Vannesse, 2011), from which the start of 9terracotta pipelines with a pressure driven flow can be observed.

In line with these previous studies, the objective of the workpresented in this paper is to further analyze the use of water in thecity of Apamea, during the Byzantine period. More precisely, weaim:

� To describe, from an archaeological point of view and using fluidmechanics, three hydraulic systems (two nymphaea, or monu-mental decorative fountains, and a private bath), excavated inthree houses located in the southeast of the city and whichbelonged to a large residential area (see Fig. 1). These housesshow a substantial level of preservation. By hydraulic system,we mean a system where water is flowing through a canaliza-tion from a cistern to a basin, as depicted in Fig. 2. These systemswere built and operated during the Byzantine period. It is worthmentioning that most of the archaeological data presented inthis paper have never been published before.

� To highlight the similarities between these systems, but alsotheir differences.

� To propose a brief interpretation of the development of this kindof hydraulic systems regarding the private architecture evolu-tion in Late Antiquity (fifth and sixth centuries AD).

� To analyze whether the cisterns of these hydraulic systems weresupplied by rainwater or by water coming from the inneraqueduct.

� To discuss the results of this analysis regarding the evolution ofwater use in Apamea in the Byzantine period.

The cisterns of these three hydraulic systems were previouslyunderstood (Balty, 1987) as being dedicated to collect rainwater.Due to partial excavations, they were not interpreted as belongingto larger systems (nymphaea and baths), which is demonstratedclearly by the descriptions in section 2 of this paper. Before theexcavations of the hydraulic system in the northeast part of the City,

Fig. 2. Schematic representation and characteristics parameters of the analyzed hy-draulic systems.

M. Vannesse et al. / Journal of Archaeological Science 46 (2014) 245e254 247


it was believed that the aqueduct was no longer operated at thetime these cisterns were built.

The analyzed systems are described in Sections 2 and 3 of thepaper. The similarities and the differences between these systemsare discussed in Section 4.1. An interpretation of the developmentof this kind of systems in Apamea during Late Antiquity is proposedin Section 4.2. In Section 4.3, the way water was supplied to thesesystems is discussed. Finally, in Section 4.4, the results of thisanalysis are discussed regarding the evolution of water use inApamea in the Byzantine period.

2. Archaeological description of the analyzed systems

The three considered houses are located in the southeast of thecity and belong to a large residential area (see Fig. 1). Their originalimplantation refers to the large urban development that Apameahas known after the major earthquake of December 13th 115 ADthat struck the whole region, as shown by their perfect inclusion inthe orthogonal city plan. These are wealthy houses, with largereception areas, organized around a peristyle, i.e. a central court-yard surrounded with 4 columned porticoes. Archaeological exca-vations have shown that these buildings were extensively restoredand embellished in the Byzantine period, until at least themid sixthcentury AD.

The description of the three analyzed hydraulic systems ispresented in this section. It is worth to mention that it is the bestavailable characterization that can be proposed.

2.1. House of Capitals with Consoles

The House of Capitals with Consoles (approximately 5000 m2)has a huge rectangular water cistern (R in Fig. 3) located in thesouth end of its large rectangular peristyle (A in Fig. 3). Built in amixed masonry with an alternation of a layer of rubble stone andthree layers of bricks, forming an opus mixtum typical of theByzantine period, this cistern is 14.45 m long, 3.00 m width (innerdimensions), with a wall thickness between 0.93 and 0.95 m, whileits maximum preserved height is 1.98 m. In its current state, thecistern could thus contain approximately 86 m3 of water. It fed asmall basin built against the north face of the cisternwith the samemasonry (see Fig. 4). This basin is 4.98 long, 2.00 m width (innerdimensions) and had a maximumwater height of 0.72 m. The basinfloor shows a small declination that has not been characterized. The0.95 m long canalization that brought water from the cistern to thebasin is nowmissing, but was enclosed in an aperture in the cisternwall, located 0.69 m above the cistern floor and 1.24 m above thebasin floor (see Fig. 4), and with a section of 0.05 m on 0.06 m. Thisnymphaeum, whose construction required the removal of columnsof the west and east porticoes, is contemporary with the refectionof the peristyle pavement (Vannesse, in press).

2.2. House of Pilasters

A small nymphaeum is installed in the secondary courtyard (I inFig. 5) of the House of Pilasters (approximately 1800 m2), openingon the east side of the main reception room (A in Fig. 5). Thisdecorative fountain has a sigma-shaped basin (see Fig. 6). It is1.70 m long, 0.80 mwidth (inner dimensions). It lies on a courtyardwall and it was built with courses of brick and stone, dating back tothe Byzantine period. The floor of the basin is missing and themaximum water height in the basin was approximately 1 m. Twolow benches flanked the structure and the only one preserved, onthe north side of the basin, features a white mosaic floor. Anoutflow canalization was installed in the pavement in front of thebasin (see Fig. 5), which tends to prove the contemporaneousness

of the two realizations. The basin was supplied with water flowingthrough a 0.70 m long cylindrical terracotta canalization of 0.12 min diameter, located approximately 2.20 m above the bottom of thebasin (see Fig. 6), and originating from a small cistern (Rb in Fig. 5).This cistern is heightened; its bottom is approximately 1.45 mabove the basin bottom. This cistern is 2.40 m long, 1.14 m width(inner dimensions). The maximum preserved inner height of thecistern is 1.50 m. Made of a mixture of brick and stone, the westwall of this cistern, at whose center is the pipe, is niche-shaped. In asecond phase (sixth century AD), a latrine (Rc in Fig. 5) is builtagainst the south wall of the cistern. It was supplied in water by acanalization collecting the basin overflow. A second cistern (Ra inFig. 5), 2.35m long,1.21mwidth (inner dimensions), whose bottomis not preserved, was also added, interlocking between the firstcistern and a room from the contiguous house. The connectionbetween the two cisterns is lost, but this addition was likelyintended to deal with a decrease of the urban water adduction(Vannesse, in press).

2.3. Triclinos Building

Finally, an isolated building lies approximately 100 m to thesouth of the House of Pilasters. It flanks the Eastern Cathedral. It isthe biggest private building known in Apamea, because its ground

Fig. 3. House of Capitals with Consoles.



area reaches up to 6000 m2. This construction, called the TriclinosBuilding, has a small bath (of about 250m2) located in its northwestcorner (Vannesse, 2014a, in press). Dating back to the Byzantineperiod, because it is subsequent to a fire that damaged this sectorduring the fourth century AD, the main cold room (E in Fig. 7) has 2apse-shaped basins built in its north and east sides. The north one,the largest, is 3.55 m long, 1.64 m width (inner dimensions) andpaved with ceramic tiles in its last phase (Fig. 8). The maximumwater height in the basin was approximately 1 m while themaximumwater volume was close to 6 m3. This basinwas suppliedwith water flowing through a 1.40 m long cylindrical clay canali-zation of 0.12m in diameter, located 1.15 m above the bottom of the

basin (see Fig. 8), and originating from a cistern (G in Fig. 7). Thiscistern is slightly heightened; its bottom is 0.28 m above the basinbottom. This cistern is 1.83 m long, 1.76 m width (inner di-mensions). The maximum preserved inner height of the cistern is1.47 m. Its masonry is made with an opus mixtum. The cold basinhas a terracotta outlet of 0.12 m in diameter in its east wall. At leastthree additional cisterns (I, J and H in Fig. 7) were successively builta few meters northwards, but without any visible existingconnection. They could be a sign of water adduction problems.

3. Mathematical description of the operation of the threeanalyzed hydraulic systems

The following parameters, characteristics of each analyzed sys-tem, are defined (see Fig. 2):

� He: water height in the cistern� He,max: maximum water height in the cistern, according to thearchaeological excavations

� Ut: inner ground area of the cistern� Vmax: maximum water volume in the cistern, according to thearchaeological excavations. Vmax ¼ He,max Ut

� Hc: height difference between the canalization and the bottomof the cistern

� f: inner diameter of the canalization� Lc: length of the canalization� v: velocity of the water jet leaving the canalization� vmax: value of v when He ¼ He,max� Q: water flow rate that had to supply the cistern in order tomaintain awater height equal toHe in the cistern. Qwas also theflow rate of water leaving the cistern when the water height inthe cistern was equal to He

� Qmax: value of Q when He ¼ He,max

� Hf: height difference between the water level in the basin (whencompletely filled with water) and the canalization

� Lf: horizontal distance between the impact of the jet in the basin(when completely filled with water) and the canalization

� Lf,max: value of Lf when He ¼ He,max

Fig. 4. House of Capitals with Consoles. Basin built against the north face of the cistern.

Fig. 5. House of Pilasters.



Fig. 6. House of Pilasters. Sigma-shaped basin of the decorative fountain. The canalization providing water to this basin from a cistern located at the back of the picture can also beobserved.

Fig. 7. Triclinos Building and below the private bath.



� Lf,edge: horizontal distance between the impact of the jet in thebasin (when completely filled with water) and the canalization,if the jet reached the limit of the basin

� te: time needed to reach awater height in the cistern equal toHc,starting from a water height equal to He,max, if the cistern wasnot fed with water. It is the operation time of the system if it wasnot supplied with water.

According to basic principles of hydraulics (Lencastre, 1995), thefollowing equations can be written:

v ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2gðHe � HcÞ

CT

s(1)

Q ¼ pf2

4

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2gðHe � HcÞ

CT

s(2)

Lf ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2gðHe � HcÞ

CT

s ffiffiffiffiffiffiffiffiffi2Hf

g

s(3)

te ¼ 8Ut

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiHe;max � Hc

pf2

s ffiffiffiffiffiffiCT2g

s(4)

where g is the acceleration of gravity (9.81m/s2) and CT is the globalpressure drop coefficient of the water flow in the canalization, thatcan be evaluated as follows (Lencastre, 1995):

CT ¼ 32þ f

Lcf

(5)

where f is the friction coefficient of the canalization, that can betaken equal to 0.04 for a typical Roman terracotta canalization(Haut and Viviers, 2012).

In reality, the flow through such canalizations of approximately1 m long, with a free overfall stream into a lower basin, would

probably not have a full flow exit jet (as shown in Fig. 2), but ratherundergo a transition into a partial flow somewhere along the lengthof the canalization, with an airspace above the water surface. Thiswould mean that the jet would have a velocity a bit higher than theone calculated with Equation (1) and would have an impact point abit further to the left than the one calculated with Equation (3).Also, some elaborate spigots (like lion heads) might once haveexisted at the terminus of the canalization to add to the elaborationof fountains and baths. If so, the contraction of the flow induced atthe exit orifice would have made the velocity of the water jet a bithigher than the one calculated with Equation (1).

Such considerations show that the Equations (1)e(4) provideonly a close approximation to reality, but they are the best equa-tions that can be proposed to describe the hydraulic systems, due tothe information available.

Using these equations and the data collected on the field, thefollowing table can be established:

The water jet in the analyzed hydraulic system in the House ofCapitals with Consoles arrived almost in the middle of the basinwhen He ¼ He,max, as Lf,max is close to Lf,edge/2.

The water jet in the analyzed hydraulic system in the House ofPilasters arrived almost at the edge of the basin whenHe ¼ He,max, as Lf,max is equal to Lf,edge. A water jet arriving in themiddle of the basin (Lf ¼ 1.00 m) would have been obtained witha water height in the cistern (He) equal to 1.1 m. This can becalculated with equation (3). This situation is depicted in Fig. 9.To maintain this water height, the cistern should have been fedwith 23 L liters of water per second. This can be calculated withequation (2). It can also be calculated with equation (3) that,when He ¼ 0.9 m, the water arrived at the eastern limit of thebasin (Lf ¼ 0.60 m). He ¼ 0.9 m is thus the minimum water heightin the cistern needed for the good operation of the nymphaeum.To maintain this water height, the cistern should have been fedwith 14 L liters of water per second. This can be calculated withequation (2).

Regarding the analyzed hydraulic system in the Triclinos Build-ing, if the water height in the basin was maintained equal to He,max,the flow rate of water leaving the cistern was equal to 28 l/s. It

Fig. 8. Triclinos Building. North apse-shaped basin in the main cold room.



means that, in this situation, it took approximately 4 min to fillcompletely the basin with water.

4. Discussion

4.1. Similarities and differences between the analyzed hydraulicsystems

The three analyzed hydraulic systems present constructionsimilarities, but also differences.

Opusmixtum, a type of masonrywidespread in the region in LateAntique period, is used for the three systems.

The calculated velocities of the water jet in the three analyzedsystems are quite close to each other (approximately 3 m/s). Asthese three water jets were submitted to the same vertical accel-eration, it implies that they had similar parabolic shapes (see Fig. 9).However, the water jet in the hydraulic system in the TriclinosBuilding was less impressive than the jets in the two other systems.Indeed, Hf ¼ 0.15 m for the hydraulic system in the TriclinosBuilding, compared to Hf ¼ 0.52 m and Hf ¼ 1.2 m for the systems inthe House of Capitals with Consoles and the House of Pilasters,respectively.

The cistern in the House of Capitals with Consoles is by far largerthan the cisterns in the two other systems. This difference betweencistern sizes could be explained by an architectural choice. Twocisterns were hidden because they belonged to the reception area(House of Pilasters and Triclinos Building) and the third one wasmonumentalized, as a consequence of the disproportion of theHouse of Capitals with Consoles peristyle, as it served as a deco-rative feature.

The flow rate of water leaving the cistern of the nymphaeum inthe House of Capitals with Consoles was by far smaller than theflow rate of water leaving the cistern of the nymphaeum in theHouse of Pilasters. This is due to the small canalization diameterused for the nymphaeum in the House of Capitals with Consoles(5 cm, compared to 12 cm in the two other systems). Indeed, it canbe observed in Equation (2) that the flow rate of water leaving acistern is proportional to the square of the canalization diameterand to the square root of the water height above the canalization(same order of magnitude for the two analyzed nymphaea). Thissmall flow rate, combined with the large size of the cistern of thenymphaeum in the House of Capitals with Consoles, explains why te

is large for this hydraulic system, compared to te for the two othersystems (see Table 1).

Regarding the House of Capitals with Consoles and the House ofPilasters, a good agreement is observed between the different di-mensions of the systems (basin width, position of the canalization,maximumwater height in the cistern). Indeed, these two hydraulicsystems presented a water jet arriving in the basin. This probablyhighlights the existence of good practice rules in the construction ofnymphaea.

4.2. Interpretation of the analyzed hydraulic systems regarding theprivate architecture evolution in Late Antiquity

In terms of private architecture, these three hydraulic systemsshould not be viewed as a unique process, as they belong to therenewal of the amoenitas (embellishment) of the Apamean housesduring the fifth and sixth centuries AD. They were planned in theframework of major transformations, and the pattern that emergesfrom the few houses that have now been explored suggests thatthere was probably no precise period for building these hydraulicsystems. Rather, they spread gradually via major projects scatteredover time, such as the installation of a new floor in the peristyle(House of Capitals with Consoles) or the rehabilitation of a wholearea (House of Pilasters and Triclinos Building). This is a clear evi-dence of their emphasis in expressing the householder wealththrough the display of water in themain reception areas (nymphaeaand private bath), as it is documented elsewhere in Roman andByzantine territories during Late Antiquity (Vannesse, in press).

4.3. Water supply to the three hydraulic systems

It seems clear that the hydraulic systems analyzed in this paperwere, at least when they were constructed, supplied either withrainwater collected on the surroundings roofs or by water comingfrom the inner aqueduct. Indeed, as evaluated in the twentiethcentury, the annual precipitation in Apamea is between 500 mmand 700 mm (Métral and Métral, 1979). These authors report anannual precipitation of 500 mm for the Jebel Zawiyé (a smallmountain 1 km to the north of Apamea) and of 700 mm for the Al-Ghab plain (a 3 km long and 12.1 km wide fertile depression nearApamea). Therefore, it would have takenmore than two years to fillthe cisterns of these systems with water, if their only water sourcewas rainwater collected on their own surface.

If the inner aqueduct continued its course straightforward to-wards the south of the city with the same slope, it can be evaluatedthat its bottom would have been approximately 5 m above groundlevel in the area of the three considered houses. The water heightinside the inner aqueduct was approximately 1 m. Therefore, ac-cording to the dimensions of the hydraulic systems analyzed in thispaper, the height difference (DH) between the level of water insidethe inner aqueduct in the area of the considered houses and thelevel of water in a cistern completely filled would have been be-tween 3 m (House of Pilasters) and 4 m (Triclinos Building). Theshortest distance between the inner aqueduct and the analyzedhydraulic systems would have been between 130 m (House ofCapitals with Consoles) and 350 m (House of Pilasters).

Fig. 9. Schematic representation of the flow in the nymphaeum in the House of Pi-lasters, when the water height in the cistern is equal to 1.1 m.

Table 1Characteristics parameters of the three analyzed hydraulic systems.

He,max (m) Ut (m2) Vmax (m3) Hc (m) f (m) Lc (m) vmax (m/s) Qmax (l/s) Hf (m) Lf,max (m) Lf,edge (m) te (min)

House of Capitals with Consoles 1.98 43.4 86 0.69 0.05 0.95 3.3 7 0.52 1.1 2.00 284House of Pilasters 1.50 2.74 4.1 0.75 0.12 0.70 2.9 33 1.2 1.4 1.40 2Triclinos Building 1.47 3.22 4.7 0.87 0.12 1.40 2.4 28 0.15 0.4 1.64 2



As mentioned in the introduction, there are archaeological ev-idences of branches (terracotta pipelines with a pressure drivenflow) constructed during the Byzantine period and starting fromthe inner aqueduct, in the northern part of the city. There is also thearchaeological evidence of a water distribution table found in thesouthern part of the city, which was probably operated during theByzantine period. The following equation can be used to evaluatean order of magnitude of the volumetric flow rate of water (Q) thatwould have been delivered by a terracotta pipeline with a pressuredriven flow from the inner aqueduct to the cistern in one of theanalyzed hydraulic systems (Lencastre, 1995):

12r

�4QpD2

�2 fDL ¼ rgDH (6)

where r (¼1000 kg/m3) is the volumetric mass of water, D is theinner diameter of the canalization, f is the friction coefficient of thecanalization and L is the length of the pipeline.

D ¼ 16 cm has been reported for the canalizations starting fromthe inner aqueduct in the northern part of the city, and f ¼ 0.04 hasbeen evaluated (by Computational Fluid Dynamics) for these can-alizations (Haut and Viviers, 2007).

Using equation (6) with L between 130 m and 150 m, DH be-tween 3 m and 4 m, f ¼ 0.04 and D ¼ 16 cm yields Q between 20 l/sand 30 l/s. As mentioned in the previous section (see Table 1), theseflow rates would have allowed keeping a nearly constant waterlevel in the cisterns of the analyzed hydraulic systems, allowingtherefore a continuous operation of these systems, during hours.

As the flow rate of water in the inner aqueduct was approxi-mately 500 l/s, approximately 20 systems like those analyzed inthis paper could have been used simultaneously if they were sup-plied by the inner aqueduct. There were dozens of this kind of largewealthy houses in Apamea during the Byzantine period (Vannesse,2011). But, even if all these houses had this kind of hydraulic sys-tem, theywere probably notmeant to be operated at the same time.

In conclusion of this part of the analysis, it appears that it wastechnically feasible to establish connections between the inneraqueduct and the three considered houses, mainly composed ofterracotta pipelines probably running on houses roofs, and deliv-ering adequate flow rates for a continuous operation of the threehydraulic systems, during hours.

If the three hydraulic systems were supplied with rainwatercollected on the entire roof of the house they belonged to, theycould be filled numerous times a year: approximately 35 times forthe House of Capitals with Consoles, 250 times for the House ofPilasters and 750 times for the Triclinos Building, assuming anannual precipitation of 600 mm and that the collecting area wasequal to the house ground area (which is an overestimation, asthese houses had usually an uncovered courtyard that could reach athird of the house ground area). However this supply would havebeen highly irregular during the year. Indeed, rains, which can besometimes violent, occur mainly during the winter season inApamea (November to April).

When it was not raining, the systems would not have beensupplied with water during their operation. The duration of such anoperation, starting from a cistern completely filled with water,would have been te (see Table 1). Except for the House of Capitalswith Consoles (for which te is larger than 4 h), te is small (close to2 min).

When it was raining, it can be easily evaluated that the pre-cipitation rates that would have allowed keeping a nearly constantwater level in the cisterns of the analyzed hydraulic systems (i.e.precipitation rates leading to supply rates of the cisterns close tothe values of Qmax given in Table 1), and therefore a continuous

operation of these systems during hours, correspond to a moderaterain (precipitation rate >5 mm per hour, for the House of Capitalwith Consoles), a heavy rain (precipitation rate >10 mm per hour,for the Triclinos Building) or even a violent rain (precipitation rate>50 mm per hour, House of Pilasters), assuming that the collectingarea was equal to the house ground area.

The hydraulic system in the Triclinos Building is part of a bathcomplex. The basin needed approximately 6 m3 of water to be filledcompletely. The cistern contained approximately 5 m3 of waterwhen it was completely filled. However, only the volume of waterabove the canalization ((He,max � Hc)Ut ¼ approximately 2 m3)could be used to fill the basin. It means thus that 4 additional m3 ofwater were needed to fill completely the basin. These 4 additionalm3 of water would have been available only when it was raining.

In conclusion of this part of the analysis, it seems that, if theanalyzed systems were supplied with rainwater collected on theentire roof of the house they belonged to, they could have beenused numerous times a year, but during a very short amount of timeif it was not raining (except for the House of Capitals with Con-soles). When it was not raining, it would have been impossible tocompletely fill the basin in the hydraulic system in the TriclinosBuilding, part of a bath complex, even if the cistern was completelyfilled with water. When it was raining, the hydraulic systems couldhave been used sometimes continuously during hours, but thatwould have happened on a very erratic basis, depending on theweather conditions, and mostly during winter.

We think that this analysis highlights the fact that the threeanalyzed systems were probably supplied with water coming fromthe inner aqueduct. It cannot be firmly demonstrated, but the so-lution of a water adduction from the inner aqueduct appearstechnically feasible and more coherent with the desired use ofthese systems than the solution of a supply with rainwatercollected on the roof surface (certainly for the House of Pilastersand the Triclinos Building).

Finally, it is worth to mention that there is no archaeologicalevidence of water input channel or pipe on any part of the cisternsof the analyzed hydraulic systems. Whatever the way water wassupplied to the cisterns (adduction from the aqueduct or collectingrainwater on the house roofs), these features would have beenlocated near the upper part of the cisterns that is missing now.However, this lack of archaeological evidence is not of significantimportance for the present discussion, as the description of such awater input would not have allowed discriminating a water supplymethod from the other.

4.4. Interpretation of the analyzed hydraulic systems regarding theevolution of water use in Apamea during the Byzantine period

By stressing highly probable evidence about a prolongation ofthe inner aqueduct towards the south of the city and about con-nections between this inner aqueduct and nymphaea and baths inthe southeast area of the city, the data presented in this work are ofhigh significance for Apamea. Indeed, the last unearthed pillars ofthe inner aqueduct are near the center of the city (see Fig. 1) and,except for the distribution table mentioned in the introduction, nodocumented information about water adduction is available for thesouthern half of the city.

The three analyzed cisterns belong to larger hydraulic systems.Therefore, it can be argued that the spread of cisterns in theByzantine Apamea is not the sign of a lack of water as the result ofthe abandonment of the aqueduct, as it has been believed previ-ously (Balty, 1987). It seems even to be the contrary, the con-struction of these cisterns is a probable sign of the operation of theinner aqueduct, supplying at least a large part of the town withwater. Therefore, the analysis presented in this work allows



renewing our conception of water adduction in Apamea during theByzantine period.

At some point in time, the city must have had to cope with watersupplyproblems, although it isunclear towhatextent. In theHouseofPilasters and in the Triclinos Building, secondary cisterns were built,close to those feeding the nymphaeum and the cold pool. Relativechronology suggests that these modifications, constituting a preludeto autarky, shouldnot beplacedbefore themiddleof the sixth centuryAD. Excavations led in the northern baths have shown that thenortheast area was still fed by running water until the beginning ofthe seventh century AD (Paridaens and Vannesse, in press).

5. Conclusion

In this paper, three hydraulic systems (two nymphaea and aprivate bath), excavated in three houses located in the southeast ofthe city of Apamea and operated during the Byzantine period, aredescribed from an archaeological point of view and using fluidmechanics.

The cisterns of these three hydraulic systems were previouslyunderstood as being dedicated to collect rainwater. They actuallybelonged to larger systems (nymphaea and baths) and were notmeant to simply collect rainwater.

The similarities between these systems, but also their differ-ences, are highlighted. This comparison stresses the existence ofprobable Roman good practice rules in the construction of nym-phaea. There was probably no precise period for building thesehydraulic systems. They spread gradually via major projects scat-tered over time, as they belong to the renewal of the amoenitas(embellishment) of the Apamean houses during late Antiquity.

The data presented in this work highlights highly probable ev-idence about a prolongation of the inner aqueduct towards thesouth of the city and about connections between this inner aque-duct and nymphaea and baths in the southeast area of the city.These are valuable results, as no documented information aboutwater adduction is available for the southern half of the city ofApamea, except for the distribution table mentioned in theintroduction.

Finally, this work is a new illustration of the fact that a combi-nation of classical archaeological approaches and fluid mechanicsanalysis allows a deep understanding of the operation of ancientwater systems.

Acknowledgments

The authors acknowledge the Fonds de la Recherche Scientifiquee FNRS and the «Centre de recherches archéologiques (CReA) » ofthe Université Libre de Bruxelles for their financial support. Theauthors also wish to express their gratitude to all the Syrianworkers that were involved in the excavations in Apamea.

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Analysis of three private hydraulic systems operated in Apamea during the Byzantine period

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