ROMAN VAULTING AND CONSTRUCTION IN THE PELOPONNESE CASE STUDIES
3.1 Argos
3.1.1 The Great Hall of the Cult Complex (Bath A)
GPS coordinates: 37°37’52.23”N; 22°43’11.07”E
Basic bibliography: Preliminary reports in BCH: R. Ginouvès (BCH78 (1954), 173‐175; BCH79 (1955), 323‐
328) and P. Aupert (BCH97 (1973), 490‐500; BCH98 (1974), 764‐782; BCH99 (1975), 699‐703; BCH100 (1976), 747‐750; BCH101 (1977), 667‐671; BCH102 (1978), 773‐776; BCH104 (1980), 689‐694; BCH105 (1981), 899‐902; BCH106 (1982), 637‐643; BCH108 (1984), 850; BCH110 (1986), 767‐771; BCH111 (1987), 597‐603; BCH112 (1988), 710‐715; BCH113(1989), 711‐717; BCH114 (1990), 858‐866). Articles:
AUPERT1985a, AUPERT1985b, AUPERT1987, AUPERT1994, AUPERT2001; LANCASTER2006; LANCASTER2009a; P.
VITTI2009; LANCASTER2010.
Plates: 2‐3‐4
Fig. 3.1 Argos. Restored view of the Great Hall with construction details
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with the vertical‐brick technique (see § 4.2.4) and a cavity was left between the brick vault and the con‐
crete gable which covered the hall.
The building was located in a central area between the agoraand the theatre (Fig. 3.3) and occupied an extended area of ca. 85 x 44 m. The French team which has been excavating the building since 195310 has documented continuous use of the building up to the 6thcentury, when it collapsed. The first phase (fig. 3.4) dates between the last decade of the 1st century to early 2nd century, depending if accepting the dating by P. Aupert (±100) or L. Lancaster’s pro‐
posal, who postpones the construction to Hadrian, based on a review of all available information com‐
ing from the publications and from autoptic inves‐
tigation11. Along the main longitudinal axis there was a rectangular court with a raised peristyle with an arched colonnade12, and a staircase13leading to the Great Hall, the latter accessed from a vestibule with two side rooms. Critical for the interpretation of the first phase is the absence of remains of an en‐
trance on the main axis. In the second phase (fig.
3.5‐A), dated to Hadrian, the court was occupied by a bath complex (Bath A), which had its hypocausts, furnaces and service corridors located in the low court (2.90 m lower than the peristyle). Water for this huge baths must have been provided from the contemporary aqueduct that had a nymphaeum‐
water reservoir only 200 m north from the bath complex (see §3.1.5 and §3.1.6). The great hall un‐
derwent substantial modifications, though main‐
taining a sacred character14: the side niches were filled (fig. 3.11), the entrance wall was demolished and jointed to the vestibule with a colonnade, while the marble decoration was renewed. In the third phase (Gordian III) the free standing hall was flanked by two rooms and the entrance ramp renew (fig. 3.5‐B). The additions can be clearly identified because they were built in opus mixtum(fig. 3.6‐C).
In the fourth phase the building was dedicated to the Christian cult15.
Roman vaulting and construction in the Peloponnese: case studies 39
Fig. 3.2Argos. Viwe of the great hall from east
Fig. 3.3 Argos. Plan of the agora and the slope of the Larissa hill during the Roman imperial period
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Fig. 3.4 Argos. Restored plan of the first phase of the cult complex
Roman vaulting and construction in the Peloponnese: case studies 41
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Fig. 3.5 Argos. Restored plans of the second and third phase of the cult‐complex (bath A)
two end walls (1 m), since they had to support the vault. Triangular bricks were cut from square ped- ales (tetradoron) 29 cm long. The pedales had a groove on the diagonals to facilitate the cutting pro‐
cedure. Uncut bricks were used for the bonding courses, the cornices and to cover the putlog holes.
Bonding courses were realised with two layers of bricks and were ca. 2 RF (Roman feet) apart (fig.
3.10). They occur at different heights than the put‐
log holes, thus they were not placed to level the con‐
Description of the hall
The hall measured 10.58/10.67 x 12.79 m and was covered by a coffered barrel vault16(pls. 2 and 3).
On the opposite end to the entrance there was an apse (Fig. 3.8) with a raised floor, above a crypt. This crypt was rectangular in plan ( 4.90 x 3.09 m) and was covered by a barrel vault (Fig. 3.8‐D); its floor was 1.5 m lower than the one of the hall.
The concrete walls were faced with triangular bricks. The side walls (1.38 m) were thicker than the
Fig. 3.7 Argos. The Great Hall from west. Detail of the gabled exterior wall of the apse
Roman vaulting and construction in the Peloponnese: case studies 43
Fig. 3.6 Argos. The Great Hall from north. Dotted lines highlight courses of putlog holes. A) holes created to insert roof trusses in the third phase; B) brick cornice; C) Joint between the first and third phase walls
Fig. 3.10(on the left) Argos. The Great Hall. View from east of the head of the north wall: A) double course bonding‐brick courses; B) top of the wall between (B1) and (B2); C) Top of the wall of room (B1); D) Impost of the arch covering the passage‐
way between (B1) and (B2); E) Impost of the second phase arch inserted when the wall separating (A1) from (B1) was removed;
F) brick facing protruding from (G) with its top surface inclined as the gable of room (B2); G) exterior wall of room (A1) topped by an inclined cornice
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Fig. 3.8 Argos. View of the apse in the Great Hall. A) front arch of the apse; B) crack in the concrete of the half‐dome of the apse; C) relieving arches above the crypt; D) crypt; E) brick li‐
ning of the wall facing the cavity above the half‐dome
Fig. 3.9 Argos. Detail of the crypt in the Great Hall. A) relieving arch above the crypt; B) remains of the solid‐brick vault; C) con‐
crete set above the solid‐brick vault; D) impost of the solid‐brick vault. (by courtesy of L. Lancaster)
struction, but only to bond the two brick facings and stiffen the concrete. Concrete was made with cae- mentaof calcareous stones set in horizontal layers as thick as the bricks.
Sesquipedales(44 cm long) were used to create solid brick arches to cover the niches (fig. 3.11).
The half-dome apse
The apse located at the end of the hall was not rounded from the exterior but squared, with a gabled roof (fig. 3.7), ca. 7x4 m in plan and 13.20 m high. The half‐dome which covered the apse was made with pedalesset radially (span 5.60 m) and concrete, set against the solid brick vault. Towards the hall, the apse had a double arch, the interior one forming the front of the brick half‐dome and the ex‐
terior an additional arch made with sesquipedales (figs. 3.8‐A and 3.12). The brick half‐dome has col‐
lapsed leaving the imprints of the pedaleson the concrete (fig. 3.14).
The backside of the wall forming the pediment of the gabled roof was faced with bricks (fig. 3.8‐E), which implies that not all of the extrados of the brick half‐dome was filled with mortared rubble.
Thus at the height of the crown of the brick half‐
dome and under the masonry gables of the roof there was a cavity, similar to the one above the bar‐
rel vault covering the hall (figs. 3.1 and 3.7).
The barrel vault of the crypt
The barrel vault of the crypt was made according to the vertical‐brick techlique. On the brick shell there was a concrete mass on which the curved wall of the apse was laid. Many bricks have been stolen, but some of them are preserved on the north side (fig.
3.9‐B). Bricks had a trapezoidal form (24.5/28x41x5 cm17) to reduce the joint between them. The joints between one slice and the other were not aligned (fig. 3.15). Slices were added from
Roman vaulting and construction in the Peloponnese: case studies 45
Fig. 3.11 Argos. Arch with voussoir bricks covering a niche of the Great Hall. Walling dates to the second phase
Fig. 3.12Argos. Great Hall. Detail of the exterior sesquipedalis front arch of the apse (the interior one has collapsed together with the brick shell of the vault)
A B
C D E
F
11,91m
1,06m1,06m1,32m
G
10.60 m 40°
66°
35°
7,11m
1,37m 0,94m
A PUTLOG HOLES
B MORTARED RUBBLE FILLING (0-35°)
C MORTARED RUBBLE FILLING SEALED BY THREE BRICK COURSES (35-40°)
D MORTARED RUBBLE WALLS WITH BONDING COURSES
E CONCRETE GABLE OF THE ROOF SPANNING ON THE RUBBLE
WALLS
F CONCRETE GABLE OF THE ROOF LAID ON THE BRICK VAULT
G PEDALES BONDING COURSES
PV rest. 2013
100 cm
D
F
PV rest. 20132013
C E
C B
40°
66°
35°
1,37m 0,94m
1,37m 0,94m
mG
A
1,06m1,06m m m19,11
1,06m1,32m m11,7
A PUTLOG
10.60 m PUTLOG HOLES
A PUTLOG
B MO
C MO
COURSES
D MO
PUTLOG HOLES D E R A T TA R
O RUBBLE
D E R A T TA R
O RUBBLE
COURSES (35-40°) D E R A T TA R
O RUBBLE
RUBBLE FILLING (0-35°) RUBBLE FILLING SEALED (35-40°)
RUBBLEWWAALLSWITH 0-35°)
SEALED BY THREE
WITH BONDING
THREE BRICK
COURSES
E CONCRETE
A W
F CONCRETE
G PEDALES
CONCRETE GABLE S
L L A
CONCRETE GABLE PEDALES BONDI
GABLE OF THE ROOF
GABLE OF THE ROOF BONDING COURSES
ROOFSPANNING
ROOF LAID ON THE COURSES
G ON THE RUBBLE
THE BRICK VVAAU RUBBLE
T ULLT
100 cm
Fig. 3.13 Argos. Restored transverse section of the Great Hall
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west to east, since at the west end the space remain‐
ing between the last slice and the wall was filled with brick fragments.
The coffered vault of the hall
The hall was covered with a vertical‐brick vault sim‐
ilar to the one of the crypt. The bricks were similar, but the vault was much larger (crypt span: 4,90 m;
hall span: 10,60 m). The vault has collapsed, but the imprints left on the mortared rubble laid on the ex‐
trados (fig. 3.16) indicate its froom.
Early morning light reveals rectangular recesses on the mortared rubble, regularly distanced to form coffers (figs. 3.16 and 3.17). The coffers were formed through a recessed alignment of the bricks, as shown in the drawing at fig. 3.13. The mortared rubble filled an empty area which resulted between the brick vault and the wall, the latter built before the vault, in order to contain both the vault and the mortared rubble. This mortared rubble had an im‐
portant structural purpose, since it prevented the brick vault from spreading at the haunches. In fact thin vaults, such as the one we are describing (41 cm thick for 10.60 of span, ratio span/thickness 1:25,8618), typically subside due to their own weight with a flattening of the curve, due to the lowering of the crown and the raising at the haunches (see fig.
3.77). The mortared rubble was made with calcare‐
ous caementa. Small bricks were used only in the lower part, where the available thickness for the fill‐
ing was reduced (fig. 3.18‐C). Most important for the understanding of the construction process of the vault are vertical discontinuities in the mortared rubble filling, which appear at regular distances (fig.
3.19 arrows). They show that the filling was placed in sectors as wide as the coffers. The vault was built from east to west, since the first vertical discontinu‐
ity appears with the first rib of the coffered surface.
On the opposite side, furthermore, the filling is more random, showing that it was poured from above. It is also possible to document a difference in the fill‐
ing since the vertical discontinuities do not occur
Roman vaulting and construction in the Peloponnese: case studies 47
Fig. 3.15Argos. Detail of the vertical‐brick vault of the crypt in the Great Hall
Fig. 3.14Argos. View of the apse of the Great Hall with the im‐
prints of the brick shell on the concrete
Fig. 3.17 Argos. View of the Great Hall from the south. A) impost line of the vault; B) line corresponding to the top of the rubble filling with the imprints of the coffers; C) line corresponding to the top of the rubble filling without the imprints of the coffers; D) detail of the brick facing of the wall; E) cavity above the solid‐brick vault; F) second phase wall in room (A3)
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Fig. 3.16Argos. Great Hall. Imprints of the coffered brick vault on the mortared rubble filling
above the first horizontal line of coffers (fig. 3.19‐
C). The upper sector of the filling which is topped by three courses of bricks (fig. 3.1 and 3.20) was built in a second phase and it has not left marks is differ‐
ent because it did not lie against the bricks of the vault. The suggests that the first sector of mortared rubble was set in place during the construction of the vault, to fill the sector of the haunches (0°‐33°) (fig. 3.13). Once the construction of the vault was completed a layer of crushed‐brick mortar was laid over the extrados of the brick vault to give stiffness and waterproof it from accidental water leakage from the roof19. Only after completion of this phase was more filling was added in the second sector (35°‐40°). The three courses of bricks on the top of it were necessary to create a uniform horizontal sur‐
face (fig. 1). On the east end of the wall, where the brick facing is missing (figs. 3.19 and 3.20), it can be seen that these three brick courses run also above the vertical wall.
The concrete gable roof
The need for the three brick courses can be better understood when the upper part of the construction is analysed. The remains of four rubble masonry walls with brick bonding courses (fig. 3.21) show that the brick courses were used as a platform for the four walls. The 2.10 m distance between one wall and the other corresponds to the distance be‐
tween two vertical ribs in the coffering (fig. 3.4).
The walls supported a concrete slab which formed the gabled roof of the hall. The concrete slab was 26‐
29 cm thick and built on a timber formwork, laid on the top of the rubble stone walls. Timber boards were used as permanent bracing to support the con‐
crete slab during curing and hardening. Once the timber rotted the boards left the grooves in the ma‐
sonry (fig. 3.20 arrow). These concrete slabs were exceptional for Roman construction.
Commented restoration of the roofing
The drawing of the restored roofing (pl. 2) shows a
cavity between the solid brick vault and the con‐
crete gables. This cavity was not visible once the building was completed. The whole system was bal‐
anced according to a clever design in which each part was strictly related to the others and together they all contributed to achieving firm solidity.
The walls were reinforced by the two‐layered bond‐
ing courses. The recess at the height of the impost was necessary for the construction of the vault, since it created the surface on which the impost of the vault was laid. The completion of the elevation of the wall before the construction of the vault (fig.
3.22‐I) was necessary to contain the lower part of the vault while it was being built. In fact the area be‐
tween the brick shell and the wall was filled during construction by mortared rubble necessary to block any possible deformation of the thin vault (fig. 3.22‐
Roman vaulting and construction in the Peloponnese: case studies 49
Fig. 3.18Argos. Detail of the northeast corner of the wall of the Great Hall. A) putlog hole walled with bricks before the con‐
struction of the vault; B) remains of the trapezoidal bricks of the vault; C) mortared filling set in the cavity between the solid‐
brick vault and the vertical wall; D) mortar with the imprints of the trapezoid bricks of the vault.
Fig. 3.19Argos. Detail of the mortared filling between the solid‐brick vault and the vertical exterior wall of the Great Hall. A) mortared filling made with broken bricks; B) mortared rubble filling. Arrows highlight discontinuities due to the construction process. Each discontinuity is as wide as a coffer. C) rubble mortared filling topped with three brick courses
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Fig. 3.20 Argos. Detail of the concrete gable of the Great Hall. The arrow points to the groove left by the formwork laid on the top of the walls
Roman vaulting and construction in the Peloponnese: case studies 51
Fig. 3.21 Argos. Detail of the cavity in the roof of the Great Hall. A) reconstructed modern wall; B) original mortared‐rubble wall with brick bonding courses
II). Once the vault was completed it was covered with the crushed‐brick mortar to make it stiffer. In fact it is possible that the crushed brick mortar re‐
alised a uniform capping that, because of the strength of the mortar, added cohesion to the brick vault.
This mortar layer somehow recalls a technique still employed today in Catalonia for particularly thin vaults, called volta de maó de plà(in Spanish: bóveda tabicada)20, where bricks are laid in layers to form thin shells and mortar is placed between one layer and the other to add cohesion and stiffness21. The filling of the gap between the vault and the wall up to the height of the wall (fig. 3.22‐III) and the top‐
ping with the three brick courses created a uniform surface for the construction of the rubble walls nec‐
essary to support the concrete slab of the gable. The gradient of the roof has been restored on the basis
of the extant gable of the apse. The crown was prob‐
ably laid directly on the vault (fig. 3.22‐IV). The four rubble walls together with the concrete were nec‐
essary to stabilise possible deformation of the vault produced by undue settlement, earthquake or if concrete creep occurred.
Remarks on the construction process
The pattern of putlog holes on the north interior el‐
evation (fig. 3.17) gives useful information on the construction process of the vault. Putlog holes were used for the scaffoldings of both the sides of the walls, since they traverse the thickness of the wall.
Some details show that the putlog holes were used for the construction of the wall and of the vault.
First it should be noted that the putlog holes con‐
tinue also above the impost of the vault, where the first two rows were never covered by the mortared
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rubble filling the extrados of the vault. Only the put‐
log hole close to the east end of the wall was care‐
fully filled with bricks (fig. 3.18‐A) while the others remained empty. This suggests that the wooden beams inserted in the putlog holes were removed after construction of the vault, and they were em‐
ployed also for the construction of the vault, proba‐
bly to lay the centering. The first putlog was filled because the centering was laid against the wall.
A second relevant observation is that of the putlog
holes being aligned with the coffers of the vault, as has been said, spaced in correspondence with the breadth between two coffers. It is possible that put‐
log holes were used first for the scaffolding neces‐
sary for the construction of the walls and then for the centering for the vault. The centering was one coffer deep, since the discontinuities in the mortared rubble filling occurred every vertical rib of the coffers22(fig. 3.19). This distance is ca. 115 cm (nearly 4 RF), that is to say ca. 16 brick arches ca. 7
Fig. 3.22 Argos. Great Hall. Scheme drawing showing the building phases of the vault
cm thick (brick 5 cm+ mortar 2 cm).
The technique using thin arches laid as rings one on the other allowed for a light centering, because the vault was not built by radial courses from the im‐
post to the crown, but by slices which adhered one against the other, from one end to the other of the room23. The reduced thickness of the mortar joint between the bricks, due to the trapezoidal shape of the brick, was important for the building process since each arch of 63 bricks had little mortar, thus it could become a solid structure in very short time and release the load from the centering24. The ben‐
efit deriving from the use of the vertical‐brick vault‐
ing technique is highlighted through the comparison with the radial‐brick vaulting used for the nearby Larissa‐Nymphaeum (see § 3.1.6) ‐dating to the Hadrianic era, i.e. few years later, and spanning 9 m‐
which needed massive timber beams to support the centering as thick as 40x53 cm.
Before the centering was moved to the following section the filling of the haunches was placed be‐
tween the arch and the wall to prevent possible de‐
formation of the vault. This sequence created the discontinuities which are still visible in the filling (fig. 3.19 arrows).
The sophisticated process of construction of the vault shows that the designer was experienced enough to achieve a prototype which, because of its two major architectural peculiarities, the width of the room and its freestanding volume, represented a new departure. The novelty of the idea makes it possible to argue that this building could be the forerunner of the introduction of vertical‐brick con‐
struction in Greece.
The prototype
The Great Hall in Argos is a case study, different not only from other buildings in the Peloponnese, but also from other vaults in Roman world. The hall had a raised apse opposite to the entrance, with a crypt underneath (fig. 3.4), and it was the first coffered barrel vault in a cult complex in Greece. The archi‐
tecture and construction are both the expression of innovative solutions which still wait to be convinc‐
ingly associated to the function.
The construction of the roofing differs from other Roman vaults in solid concrete, because between the brick vault and the concrete roof there was the cavity. The vault had a curved extrados, similar to the mausoleum RG1 in Troezen (see § 3.2.3), but in the latter it was uncovered, while in Argos it had the concrete gables. Other examples with a timber roof covering a vault with a curved extrados cannot be compared because the truss was structurally inde‐
pendent from the vault. In Argos the pitched con‐
crete roof and the vault were structurally interdependent.
The vertical‐brick vault was particularly effective to cover the nearly 11 m span vault without incur‐
ring the complexities of a solid‐concrete vault. The vertical‐brick technique had a long tradition in the East25and the person who conceived the Argos vault knew the advantages and the constraints of this technique. On the one hand the vault was very light, because of its 41 cm thickness, but on the other it needed to be properly stiffened, because of its slen‐
derness and its form26. To avoid the flattening of the curve of the vault and the spread of the haunches, the extrados was “blocked” with masonry up to the height of 40° from the impost (fig. 3.13‐B and C). At the same time the upper sector of the vault was sta‐
bilized by adding the four walls which supported the concrete roof (fig. 3.13‐D), and the concrete mass on the crown (fig. 3.13‐F). What is surprising is that the five‐hinge mechanism illustrated by Hey‐
man for minimum thickness arches is reflected into the five sectors of the brick arch: from the impost to the haunches, from the haunches to the end of the cavity and from the end of the cavity to the crown27. It is unclear how such a peculiar construction, em‐
ploying with considerable expertise both oriental and western building techniques, was conceived, but what is clear is that the designer was concerned about two major issues, which were skilfully re‐
Roman vaulting and construction in the Peloponnese: case studies 53