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1. Introduction

Due to the ruined state of so many ancient structures, the efforts of architects and archaeologists are essential to restitute their original appearance by means of traditional drawings, and, increasingly, using virtual techniques. However, the consideration of whether proposed reconstructions are structurally stable is often not confronted adequately. Unless physical reconstruction (anastylosis) is involved, issues of structural feasibility may not be addressed, or only indirectly by virtue of common sense and reference to comparanda. On account of the structural conservatism of many Greek trabeated buildings this situation is generally unproblematic; yet there are some cases where structural analysis can be usefully employed to validate – or not – a particular reconstruction, even one that has been widely accepted and reproduced in the literature.

2. Temple of Artemis

The Temple of Artemis on the island of Corfu, according to Gottfried Gruben, is the “first and mightiest example of developing Corresponding author: gherdt@gmx.de

stone-architecture” (Gruben 2001, 112). Erected in the early 6th century, it holds a key place in the development of the Doric order that went on to govern the appearance of so much Greek architecture. The pediment of the temple is important as the first surviving substantially complete assembly of Greek architectural sculpture. In addition the monument is striking in terms of its structure and dimensions. As reconstructed by the excavators, it measures 47.90 metres long, 22.41 m wide and about 14 m high, incorporating a complete circuit of columns (peristasis) with 8 on the ends and 17 on the flanks (Fig. 1).

The significance of the Artemision is highlighted by the fact that only a generation or two earlier the great majority of temples in Greek territories were much smaller and narrower; they were built of perishable materials and involved relatively modest spans; their appearance was characterized by ornament and sculpture that by comparison must have been much less elaborate (even if in truth we lack the information to be absolutely certain on this point). In the decades of transition between humble structures of this sort and Artemis’s impressive temple there did exist a few other temples that likewise

Structural Assessment of Ancient Building Components, the Temple of Artemis at Corfu

Georg Herdt, Aykut Erkal, Dina D’Ayala and Mark Wilson JonesUniversity of Bath, UK

Abstract: The pediment of the temple of Artemis at Corfu is one of the very earliest remains of monumental Greek construction. This temple, which dates towards the beginning of the 6th century BC (to judge from the style of the sculptures of the pediment), has suffered extensively since antiquity, leaving us with only a highly fragmented image. Excavated by Gerhardt Rodenwaldt at the beginning of the 20th century, the Artemision was reconstructed on paper by Hans Schleif, in their 2 volume publication. The reconstruction has been criticized in minor respects, but the plausibility of the pedimental sculptures in their proposed position has been generally accepted. In this paper however structural analysis suggests that the current position of these sculptures is inconsistent with stability. This triggers a revised reading of the architectural reconstruction, calling into question the whole plan, with its supposed grand pseudo-dipteral layout.

Keywords: Ancient Greece, Structural Analysis, Finite Element Method, Corfu, Conservation, Architectural Sculpture

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deserve to be called monumental. Two of the most notable are the temple of Poseidon at Isthmia (ca. 650 BC) and the temple of Hera at Olympia (ca. 600 BC). The former had a cella measuring approximately 32 m by 7.9 m, but it is unclear whether there really was a peristasis of wooden columns/posts (Gruben 2001, 106). The Heraion measures 50 m by 18.76 m and is the first building known with certainty to have had a monumental and regular peristasis, one consisting of 6 by 16 columns, though initially these were made of wood (Gruben 2001, 52). Soon after our Artemision there followed in Sicily a succession of large religious structures, some of them truly gigantic (Gruben 2001, 288). The Corfu temple was not necessarily the project that launched the new monumentality (this distinction could belong to a different building that happens to be lost to us), but it clearly stands at a critical moment in the development of Greek temple architecture.

The chief focus of this paper is the detailed reconstruction of the pedimented front of the temple and its sculpture as proposed by the excavators. The association of the sculptures with this building is not in doubt; however their capacity to bear load requires evaluation. A revised reconstruction has the advantage of being more plausible from the point of view of statics and constructional soundness, and this in turn has implications for the layout.

3. Documentation

Following excavations in 1911 to 1914, the two volume report on the sanctuary of Artemis at Corfu was published by Gerhard Rodenwaldt and Hans Schleif in 1939 and 1940. Their reconstruction of the temple and its dimensions is based on the study of two main aspects; the foundations and the sculpted pediment. Presumably because they were of little use to later builders, the sculptures were not destroyed and remain surprisingly complete. Rodenwaldt and Schleif’s restitution of their original disposition is carefully thought through and represents an important advance in the knowledge of Greek architectural sculpture. The stonework of the foundations on the other hand, was almost completely removed by later builders in the locality (Gruben 1996, 91). On this basis Schleif restores the eight columned front as 22.41 m wide, which is about 3½ m wider than the slightly older temple of Hera at Olympia. The proposed column-spacing is quite dense, with 17 columns reconstructed for the 47.90 m long flanks. Since so little is known about the substructures (the layout of the foundations being determined by the change of fill in the presumed robbed trenches – hardly the most certain method), Schleif sought to give order to the plan by applying a foot grid. The result was questioned in 1943 by Hans Riemann, who suggested a different value for the foot. However, for seventy years no doubts have been raised over the more fundamental

Figure 1. Plan of the temple of Artemis at Corfu. Figure 2. Elevation of the temple of Artemis. Existing fragments are indicated by tone.

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points of Rodenwaldt and Schleif’s work, and in particular the monumental scale of the edifice, the extent of which matches their reconstruction of the pediment (Kähler 1949, 42).

The pediment and its sculptures are indeed impressive. The Gorgon itself in the centre of the tympanon measures more than 3 m in height. The overall length of the pediment is about 20 m, though there is an element of estimation due to some missing parts (Fig. 2). Generally, the sculptural blocks are in pieces but in a good condition; many surfaces are intact, and for some blocks the outline of missing parts can be confidently reconstructed. Each block incorporates a decorated framing strip, one at the top and one at the bottom; the upper follows the pitch of the roof under the raking geison, the other sits on the horizontal geison. The decoration of these two strips is different; a chevron pattern for the upper and a meander pattern about 30 cm tall for the lower.

The sculpted taller blocks at the centre of the pediment present an increased width at the bottom, forming a stand which is preserved up to a maximum depth of about 55.5 cm. The depth of the sculptures is 17 cm at the sides and roughly 29 cm near the centre. This leaves a surplus of the stone material of 26.5 cm to form the background at the bottom. The

section steps in higher up, as can be observed at the left panther-lion, and then continues to narrow towards the top, presumably to lighten the blocks for the sake of lifting them (Fig. 3). Around the heads of the two panther-lions the stone has been trimmed down to as little as 5 cm thick behind the feline’s mane. And even worse, the block displaying the Pegasus is reported to narrow down to 4 cm (Schleif 1940, 25).

Four blocks of the raking stone geison remain, each measuring about 2 m in length. The surfaces of these stones show a series of cuttings, allowing a definite allocation of their position and that of the adjoining blocks. At their lower surface an erosion mark (67.5 cm from the front) indicates the junction with the next components. Connections were effected by means of dowels, the cavities for which still remain visible on each geison-block. The upper surfaces of the geison blocks also display a smoothed area as well as holes for connecting to the sima, with dove-tail connectors for joining each block and a large socket at the rear for the timber beams that once spanned across the porch. The smoothed surface matches the dimensions of the second sima, the marble sima, of which some elements survive. This must have substituted an earlier sima, fragments of which also survive made of terracotta and about 80 cm in height, as well as some tiles.

To define the cross-section of the pediment, Schleif placed the sculptures centrally below the raking-geison; their position is set at 67.5 cm from the front by the limit of the erosion due to weathering. The sculptures were thus sheltered from rain, but two problems arise with this position. The first concerns the sequence of construction, since the geison is placed on top of the sculptures. For this to be the case these must have been inserted into position before the roof could have been placed onto the building, the inverse of usual practice. But more importantly: Schleif’s reconstruction presumes that load from the roof can be applied to the sculpted blocks, and he supplies a section that

Figure 3. The block with of the left lion-panther according to Rodenwaldt.

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makes it look plausible (Fig. 4a). However, he does not supply a section through other blocks which have been tapered by the sculptors to the point that their structural capability must be called into doubt (Fig. 4b). Indeed it seems doubtful that Greek sculptors ever intended such a slim profile to bear load. Hence the need to test its feasibility by means of structural analysis.

For this purpose, the weight of the roof has to be assessed. The surviving blocks were combined into two alternative reconstructions by Schleif, of which one results in a lighter construction for the roof than the other. Solution A places the monumental terracotta

sima directly onto the massive geison block, while Solution B engages an additional layer in between these two components. Solution B therefore raises the sima about 25 cm, which is consistent with a decorative bead at the edge of the geison. According to Schleif it is the presence of the bead that makes Solution B more probable than Solution A (Schleif 1940, 57 Abb. 43.). However, this fill layer brings additional load onto the sculptures and the slender wall to which they are attached. In order to check the level of potential stresses, structural analysis using Finite Element Modelling has been performed. The presumed properties of the materials and loads, necessary to perform the analysis, are given in Table 1. These have been chosen from the literature (Schleif 1940, 21) on the basis of the archaeological evidence using limit conditions assumptions. In addition to the self-load, tiles have been applied as uniformly distributed loads over the roof and terracotta as a line load on the outer edge of the roof. More accurate results could be obtained by a detailed survey of the remaining fragment and characterisation of the original materials.

4. Structural Analysis

The Finite Element Method (FEM) has been used to structurally analyse the proposed reconstruction of the pediment. The model replicates the left lion-panther sculpture and the objective is to verify whether the thinner portion of the stone section would be able to withstand the roof loads as proposed in Schleif’s hypothesis B. After generating its geometry in AutoCAD, the model has been transferred into the finite element software ALGOR (Fig.

Figure 4. a) Temple of Artemis, section through the pediment at the ‘dying-giant’ (Schleif) and b) at the ‘panther-lion’ (Herdt).

Structural Materials Non-structural Materials

Properties Lime Stone

(raking

geison)

Fill Layer

(Timber,

Clay, Earth,

Pebble)

Mass

Density and

Resultant

Dead Loads

Roof Tile Cover

(Compacted Clay)

Sima

(Compacted Clay)

Uniformly

Distributed

Surface Load

Uniformly

Distributed Line

Load

Mass Density 3500 kg/m3 2200 kg/m3 Mass Density 2500 kg/m3 2500 kg/m3

Elasticity Modulus 30 Gpa 0.2 Gpa Dead Loads 2250 N/m2 25000 N/m

Poisson Ratio 0.25 0.30

Table 1. Material Properties and Loads.

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5). Meshing (discretization) has been applied, paying attention to each part in the model. As such, the sculpture and the background stone have been finely meshed to better analyse the critical thin section where higher stress concentrations are expected, while the other

parts have been assigned coarser meshes (Fig. 6). The model was constructed using 8-node 3-dimensional brick finite elements having 3 translational degrees of freedom at each node. The advantage of using these elements is to provide a complete 3-D state of stress in the stones. Boundary conditions at the base of the stone have been assumed as fixed, i.e. the base of the stone is not able to move downward under the applied load. Although this is not necessarily the case, as some deflection in

the bottom of the pediment between columns might have occurred under the weight of the stones above, the error committed is of the same order of magnitude as the other numerical assumptions in the model.

Figure 5. Model generated in AutoCAD. a) Schematic Model; b) CAD Model

Figure 6. Model geometry including the structural parts and meshing. a) Perspective View; b) Front View; c) Right-side View.

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5. Analysis Results and Discussion

The results show that the maximum displacement magnitude is as expected at the edge of the pediment overhang, a very modest 0.156 mm (Fig. 7). The critical stresses are detected at a position just below the strip decorated with the chevron, where the depth of the background stone is at its minimum.

The distribution of the maximum principal stresses shown in figure 8 demonstrates that tensile stresses are generally very low except for a concentration of stress at the necking of the block between the body and the head of the panther where the cross-section reduces. The value in this area is as high as 0.71 MPa. Values of strength for Corfu Limestone have not been found in the literature, though a typical average value for limestone

tensile strength is in the range of 1 to 2 MPa. This allows only a very modest safety factor, which would be in contrast with the usual overdesign of Doric temples. Figure 9 shows the distribution of minimum principal stresses, i.e. the value of maximum compression at any point in the stone. In general the values are very low and far from the typical compressive strength of a limestone, usually in the range between 20 and 200 MPa, for un-weathered un-fractured limestone. However it should be noted that where the cross section is reduced, just above the head of the panther, the stress is at its worst, 4.45 MPa. Given the way in which the load is transferred from the geison, performance is best simulated by considering a concentrated load over the thin slab of stone. The strength to point load of limestone, is much lower than its uniaxial compressive strength at about 2 MPa to 10 MPa, hence again creating a condition which would lead to either a very small safety factor or even failure. The results, therefore, suggest that the structural stability of the structure is not fully ensured for Schleif’s hypothesis B.

Thus numerical analysis, thanks to the 3D modelling, is able to identify the concentration of stresses resulting from the specific proposed geometry and construction, and it shows that the

Figure 7. Displacement Magnitude (Contours of resultant displacements).

Figure 8. Maximum Principal Stresses. a) Front and right-side views; b) Back and left-side views.

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sculptures would not able to bear the assumed loads. Inclusion of likely additional components not included by Schleif - for example a roof acroterion - would make the situation even more severe. Indeed such a feature might well be expected, and in this period acroteria were large and prominent and therefore heavy. The weight of any such embellishment would arrive at the edge of the verge, increasing stresses on the sculpted blocks underneath. Furthermore, if the designer of the temple intended to bring load upon these elements, he surely would not want to weaken them by tapering. Schleif’s solution opposes normal principles of craftsmanship by transmitting structural forces through fragile parts of great value, due to an artistic effort invested in the sculpture.

6. Discussion

As the structural analysis indicates, Schleif’s proposal loses credibility due to the risk of failure involving the most precious components of the building, inviting alternative solutions. Indeed, it seems more likely that the sculptures were disconnected from the structural system. This can be achieved by reconstructing the sculptures closer to the front of the pediment and placing a proper load-bearing wall at the back (Fig. 10). This relatively

minor change has significant implications. The supposed horizontal geison with an inclined leading edge has to be altered into a more typical flat-topped geison, the common shape for horizontal geisa, which would now host the sculptures up to near its edge. This in fact was the normal condition judging from later well-preserved temples (Schwandner 1985, 108).

Due to the geometry of the corner of the pediment, the modification of a shallower geison results in a more compact elevation, which would be at least 1 m shorter and could perhaps be as much as 3 m shorter. Such a reduction would require rethinking not just the façade but also the plan as a whole. A more compact elevation favours a façade with six instead of eight columns, like so many other temples of that period. A front with seven columns is also hypothetically possible. As part of his eight-column-wide proposal Schleif imagined what the Roman architect-writer Vitruvius called a pseudo-dipteral layout, and both the resulting elevation and the plan have been widely reproduced since their publication seventy years ago. A pseudo-dipteros fits within the overall envelope of a dipteral or double colonnade, except that there are no inner

Figure 9. M i n i m u m P r i n c i p a l Stresses.

Figure 10. Temple of Artemis, proposed new position for the sculptures of the pediment, divorcing them from the structural system.

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rows of columns. This involves a wide span for the peristyle; indeed at Corfu – according to Schleif – this reaches almost 5 m, which is to say substantially greater than that the span of the temple interior. Be it noted that Vitruvius writes that this pseudo-dipteral scheme for temples was only invented by Hermogenes, who worked in the early second century BC. Can we be sure that such an enterprise was possible four centuries earlier, not long after 600 BC? Greater confidence over the design of the Artemision can probably only be achieved by inspecting once more what remains of its foundations. In fact, an archaeological re-evaluation of the site now seems imperative.

7. Conclusions

This paper reveals that the hitherto accepted reconstruction of the Temple of Artemis should be called into doubt. Schleif’s solution involves putting load onto the sculptures and this does not stand up to scrutiny, nor a complete three-dimensional structural analysis using Finite Element modelling. Assessing ancient building components structurally help us find plausible positions for them. It is a tool that can be used to guide new reconstructions and anastylosis, or for scrutinizing published proposals as in this case. By combining structural analysis with attention to the archaeological details of surviving blocks it should be possible to reconstruct ancient monuments in ways that are structurally plausible.

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