Talah Alshami - Crete Prof. Diamantis Panagiotopoulos
Koumasa Tholos Tombs Construction Hypotheses Modeling Tholos Epsilon as a case study
- 2022 | Supervisor
- March - June Internship Report - Koumasa
Part IThe Modeling Process of Tholos Epsilon.
Introduction.
T he three-dimensional models of archaeological sites are gaining more and more recognition and are becoming an essential part of the understanding process for any scholar. It has a great impact on the presentation of a topic as it gives more depth to the delivery of certain information dedicated in particular to a part of the storyline of any project/ study. The internship was an opportunity to study the site of Koumasa while grasping the surrounding areas and network of villages. These relations were part of the studying of the ancient Minoan civilization and its interesting typology of buildings namely; the tholos tombs. As the covering method of this typology of structures is not confirmed and the hypotheses are still able to be discussed and questioned, I found it necessary to compare the different hypotheses in order to clarify the differences and study the possibilities of each of them, leaving the task of experimenting the feasibility of these ideas to the mathematicians, structural engineers, and, certainly, archaeologists. Therefore, building an imagery base from which further studies can take place in further detail can be useful.
Basic Observations and Description.
The Archaeological site of Koumasa is found near the road heading to Vasiliki. The site is a small agglomeration of three tombs taking a circular or quasi-circular shape along with some rectangular structures. Each of the tombs, named Tholos, is preserved at no more than 1.5 meters in height. Two of which are near 9 meters in diameter and the third is around 4.5 meters.
T
he archaeological site of Koumasa is located on the southern coast of the island of Crete. It occupies a place on the foothill of the Asterousia mountains to the north of the chain. The closest villages surrounding the site are; Koumasa, Loukia, Vasiliki, and Vagionia.
T he in-between spaces bordered by the round tholoi, when unearthed, showed a lot of findings and artifacts. These spaces are recovered by the archaeologists and got a coating on top (the green fabric in the image above). Furthermore, the archaeologists had added a cement layer to fix the stones in their places. While this attempt to preserve the tholoi might have kept their shape intact, it might also have changed some of the characteristics of the tholoi to the observer and delivered a false image of the building techniques. Of the three tholoi, tholos E is the most complete and with the clearest structure as it has still the rectangular annex part attached to it and is not fully destroyed.
s for the stone sizes, it is hard to clearly grasp a pattern in the choice of the stones. The inner surface of the tholos E wall shows larger stones in the bottom layer compared to the upper ones. While on the other hand, the outer surface of the wall doesn’t really show the same hierarchy. The stones are generally smaller and accumulated around the inner surface to form a 1.6- to 1.9-meter thick wall. In between the two surfaces, the space is filled with stones and some soil despite the current state that shows mostly soil covering the gap. Some large-size stones are placed on top of the tholos with no reference to the original location.
A
T he stones used for the tholos E range in color from light yellow to dark grey and sometimes black. Most of the Cretan soil is formed of alluvial, colluvial, and aeolian despositional cycle. We can spot some reddish-colored stones within the composition of the tholoi. “Paleosoils are usually redder in color than their younger equivalents, due to the longer period for oxidation of ferrous minerals.” The stones show an excessive amount of details of layers sometimes and can vary in color. Interestingly, some projecting stones are protruding from the outer surface of tholos E like in many other tholoi in the Mesara valley. The distance of projection is not longer than 20 centimeters or a palm span.
T he entrance of the Tholos E, just like tholos B is oriented towards the east and is defined by large upright standing slab stones supporting a massive lintel in what is called the “Trilithon Principle”. The only lintel that is preserved in the site is the lintel of the tholos A, whereas tholos B and E’s are lost. The entrance of tholos E is hardly 1 meter in width and has no trace of a door-slab pivot like the one of tholos B. The sizes of the stones in the entrance of tholos E are clearly larger than the upper layers. Attached to the entrance is the annex room or the ante-room that precedes the tholos’ inner space.
T o model a 3D visualization of the Tholoi, a simple photogrammetry method was applied. Taking into consideration the limited time and unstable weather, the photographs were taken mostly for Tholos Epsilon and the lack of equipment made the choice limited to using the phone camera. However, the results were patches of 3D point cloud generated using Agisoft Metashape and exported as meshes to both Rhinoceros to place them around the plan of the tholos, and to Blender to model the stones of the inner ring wall with an estimated depth as seeing the depth of the stones is not possible due to the cement layer added by the archaeologists to place the stones in their places.
3DandPhotogrammetrythepointcloudmesh.
Modeling the Tholos’ Stones Using Blender. B lender gives the possibility of easily carving and shaping irregular forms which makes it suitable for modeling the stones of the tholos. For that, the 3D meshes were placed in the software and a series of box-shaped meshed were placed to mimic the corresponding stones of the inner wall of the tholos. Then, the boxes were reformed accordingly to match at least the profile of each visible stone possible with its orientation. However, the depth of the stones towards the wall’s body is estimated as there is no way to see the hidden parts due to the application of cement by the archaeologists to the stones to keep them in place. Hence, this creates a suspicion around the actual position of the stones that can not be known exactly unless there was a record of the stones of the first excavation. The modeling attempted to give the stones as much natural and realistic appearance as possible.
From Blender to Rhino Appllication. A fter modeling each patch of the inner wall into stones, they were brought back to Rhinoceros to position them in the right place according to how the 3d meshes were placed at the top of the 2D plans. An attempt to give the stones their actual material was applied but not used as it will overload the software more than the personal computer can handle. Gradually the forming process of the inner ring wall of the tholos was getting completed over the course of 2 months. Since the site visits were limited to the internship duration in Koumasa, there was no chance to do more photography in order to proceed with the outer ring wall. Thus, the stones modeled for the inner wall were used to form the outer one and later in building the ruinlike 3D model of the tholos following the known hypotheses around the architecture of the Cretan tomb. However, the top part was partially covered by 3D meshes generated also from the Agisoft Metashape depending on photographs.
Tholos Alpha
Current Situation Results. n overall modeling of the tholos Epsilon was achieved. The inner ring wall was mostly built according to the point-cloudgenerated 3D mesh, the outer ring wall was modeled based on the stones of the inner one with modification of the size, and the top surface of the tholos ring is partially made of the 3d meshes and the arrangement of the stones in the gaps of these meshes. Therefore, the stones modeled for the inner ring wall were used to complete the entire shape of the tholos as well as tholos Beta with modification of the height and inclination as the tholos A has a large missing part on the southern side. The annex structure was modeled using the same stones and placed in a regular stretchers bond and headers bond. Only the left wall of the annex was built, whereas the right wall was modeled as it is shown in the documentation plans with only one layer of smaller stones above ground level.
TholosEpsilonBeta
As for tholos Alpha, it is kept as a mesh and not modeled due to the timeline restriction but it was placed with the other tholoi to give the context of the three tholoi together.
Tholos
Part IICovering Hypotheses.
AThe burial act in Crete is distinguishing the civilization of the Minoans. The usage, practice, and development are known, however not their architectural form. (Branigan, the Tombs of the Mesara, 1970) The tholos tombs have been compared to their Mediterranean parallels and particularly to the Syrian Halaf culture to the northeast of the country and in northern Iraq, as they have the same approximate diameters and overall shape. However, their function was different and the annex part attached to the Tholos is far longer than the ones of Crete. (Ibid) Generally, the form of the tholoi was discussed to be inspired by the neighboring cultures as Branigan stated, and also the archaeologists; Evans and Xanthoudides proclaimed connection and similarities to cultures of north Africa.
However, the most interesting hypothesis is the fully stone-built vault as it challenges the archaeologists due to the lack of material evidence in the sites of the tholoi, as in not finding enough amount of stones that could be sufficient for constructing the vault. Among the archaeologists who supported the first hypothesis were, Xanthoudides, P. Warren, and Y. Sakellarakis. However, other archaeologists supported the hypothesis but under certain conditions. For example, E. Stefani suggested a wooden framework to support the structure; G. Karo thought it should have been built with the help of light materials like clay; O. Pelon agreed that the smaller tholoi (less than 6 m in diameter) could have been built fully in stones but larger tholoi needed wooden support; S. Hood agreed also on stone vaults for small tholoi; C. Papadopoulos proclaims that only the periods from EMIII to MMIA could have had tholoi fully vaulted in stone, whereas the earlier ones should have had light roofs lighter However,materials.thehypotheses were set based on the study of the different tholoi in the Mesara plain, e.i., Sakallarakis who agreed on the hypothesis of the full stone vault for the Tholos C in Archanes/ Phourni, and delivered evidence for his argument. Each tholos is different in terms of its characteristics like the diameter, the attached antechamber, the height of the preserved walls, their thicknesses, and the findings in the site; and
hypotheses around the roofing of the tholoi in the western Mesara plain. These are: first, a fully stone-built vault; second, an open roof or a flat roof made of perishable materials; third, a full vault made of mud or mud bricks.
The plan of the archaeological site of Koumasa, Xanthoudides, the Vaulted Tombs of the Mesara, 1924. The drawing shows the first attempt to sketch the complete dome over the section of the tholos Epsilon.
ccording to Luca Girella in “Problems of Roofing of Early Minoan Tholos Tombs:
Hypotheses.CoveringIntroduction.
The case of Kamilari A Tholos Tomb in the Western Mesara Plain”, there are mainly three
Alternative proposal for housing. A picture from a powerpoint slide show for professor Andreas Vlahopoulos (ΒΛΑΧΟΠΟΥΛΟΣ ΑΝΔΡΕΑΣ). The porposal shows the wodden framework proposal for the covering of the tholos with two materials; high stone base and covering of mud or other light material. in terms of the state of its preservation. The tholos tombs in Koumasa are considered some of the largest in diameter in the western Mesara plain which makes it hard to decide which hypothesis is the closest to reality.
Trials.Vault-Shaping
S ince a clear drawn version of the hypotheses is lacking from the bibliography, the reconstruction relied on the sketches of the sections found, like the one of Xanthoudides for example, and the one found in a presentation for professor Andreas Vlahopoulos with no mention of the painter. To the right are images of the reconstruction that took the basic sketch of Xanthoudides as a reference and tried to build on its basis. However, the curvature of a section of the dome drawn by Xanthoudides is too inclined to be built in mere stones without any other material, like mud. Also, the proposal by P. Warren of adding a pillar in the center of the tholos looks unreasonable without much detail on how to understand the load distribution of the dome through the pillar.
The Vaults.Corbelled
(see image 3) The higher the vault goes, the smaller the size of the course and, therefore the stones, get. This resulted in the thinning of the thickness of the ring wall as the vault rises. (see images 4, 6, and 7) As to follow the hypotheses proposed by the archaeologists, a wooden framework was also applied in the vault to visually give it a supporting element.
1 2 C orbelled Vaults are understood as the polar repetition or array of corbelled arches to cover a span of space. The corbelled arch is described in “Brittanica” as: “A corbel arch consists of two opposing sets of overlapping corbels, resembling inverted staircases, which meet at a peak and create a structure strong enough to support the weight from above.”
(see images 5 and 8)
The Overturning Moment is the force that pulls the wall or the group of stones by Gravity factor down to the ground, and it works at the springline, which is the point where the wall is heading up to the apex of the vault and not constructing only vertically. At each course or raw of stones, there is a critical point of collapsing. The Resisting Moment is the opposite force that uses the dead load of the stones placed on top of each other in a corbelled sequence to prevent the collapsing of the stones that are piling up to cover the void. Therefore, the stones are placed in a position that doesn’t make the center of gravity slide to the void intended to be Thecovered.corbelling technique forms a section that has a triangular shape pointing upwards. However, with the use of smaller stones and the change of the inward offset, the curvature of the section profile can be monitored. Below are basic experiments to virtually model a corbelled structure that has different offset values and each with two-layered wall skin. (images number: 1 with a slight offset, and 2 with further offset) According to archaeologist Christian Lassure, building the corbelled vaults requires two principles: 1- The Principle of Corbelling, which is the overhanging of the courses of stones gradually as we explained, and 2- The Principle of the Outward Inclination, which is the slight slopping of the stones to the opposite side of the vault’s construction that will buttress the stones horizontally. These two principles were taken into consideration while modeling the vault over Tholos Epsilon.
Another trial was done to create a curvature that follows a corbelling method with an offset of 0.5 meters for each course of stones.
The corbelling architectural technique depends on the partial offset of courses of stones or bricks toward the center of the space intended to be covered, in our case the “vault” of the tholos. The offset should be calculated so that the overturning moment force is not larger than the resisting moment.
Whether the structure used fillers or not, at least we know by now that the first face or the inner wall of these circular structures can be built with the corbelled technique using dry stones, and the frame that encircles it plays the role of balancing the structure.
The Components of Construction.Corbelled P rofessor Borut Juvanec has put out three elements that he considers the components of corbelled construction. Those are Vaulting, Facing, and Infilling. According to him rough-cut“Thevaultingismostlymadeofcut,orunhewnflatstones.
The revetment, which also serves as counterweight,ismadeofbigstonesinthe Thebasepart,andflatstonesintheupperpart.infillingofwastestoneorrubbleoccupies bigeventhespacebetweenthetwo,andsometimescoverstheroof.Insomecases,apileofstonesmaycrownthetop.”
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S cholars, among which Branigan, drew the attention to similar structures in the Middle East namely, Syria and northern Iraq (Mesopotamia at that time). These structures were the settlements of the Halaf Culture (5th Millenium BC) that was named after Tell Halaf in Syria. (see image to the right) The most known example is the Tholoi of Arpachiyah (next page to the left.) These structures, have certainly provided good examples to compare building techniques. However, despite the similarities in plan, size, and average diameter, they differ in some aspects. The attached part of the structure (the antechamber or annex) is far longer in the Halaf culture than the ones of the Minoan culture in the Mesara Plain. Also, the Halafian structures were shrines or worshops not tombs. Some other scholars refferred to structures from the Nubian culture in North Africa around the Libyan Sea. Branigan refers to those as they were adopted by Evans and Xanthoudides. “Evanswasthefirsttosuggest a North African origin for the tombs, and he was quickly followed by Xanthoudides.”
Dwellings and settlements of the Halaf culture: a – various types of tholoi from Arpachiyah, C avi Tarlasi and Sabi Abyad; b – plan of Yarim Tepe II, level V (from Breniquet 1996: pl. 36); c – plan of Sabi Abyad, level 3 (from Akkermans 1993: fig. 3.12).
He continues: “The Libyan sepulchres had circular stone walls, rectangular antechambers (sometimes built inside the perimeter rather than outside it), trilithon doorways, and communal family burials (see nextpage image 2). Totheseparallels, Xanthoudides added the vaulted tombs of theEarlyDynasticperiodinEgypt,andboth EvansandXanthoudidesrepeatedlystressed themanyEgyptianparallelsforthematerialcultureofthepeoplewhousedtheMesaratombs”
A pagliaddiu at Santu Pietru, Corsica, France A girna in Mistra Valley, Malta
Source: Frangipane, M.. (2007). Different Types of Egalitarian Societies and the Development of Inequality in Early Mesopotamia. World Archaeology. 39. 151-176. 10.1080/00438240701249504.
A bombo near Tomelloso, Central Spain
A trullo, near Alberobello, Puglia, Italy
The following series of drawings presented by the professor show different types of corbelled structures in different European Mediterranean countries. The Mediterranean and the Arab Gulf Parallels.
https://whc.unesco.org/en/documents/139101
https://whc.unesco.org/en/documents/109739
To the right: Image 2: Three Crete,RitualArchitectureStudyOFTHEKeithTombs.AfricanNorthCircularSource:Branigan,TOMBSMESARA,AofFuneraryandinSouthern2800-1100B.C.Totheleft:Image1:ReconstructionsofArpachiyahtholoiinTT7-8(afterMallowan&Rose, 1935:Source:figs.7-12).İpek, Bahattin. (2019). Figural Motifs on Halaf Pottery: NeolithicIconographicalanStudyofLateSocietyinNorthernMesopotamia,A Master’s Thesis. Archaeological Sites of Bat, Al-Khutm and Al-Ayn, Oman https://whc.unesco.org/en/documents/139102
However, it is noteworthy to point out some other exciting architecture that might also be interesting to study and shed light on. “The protohistoric site of Bat lies near a palm grove in the interior of the Sultanate of Oman. Together with the neighboring sites, it forms the most complete collection of settlements and necropolises from the 3rd millennium B.C. in the world.” UNESCO.
Part IIIModeling CoveringOptions.
he modeling process proceeded from building the base of the current state of the tholos Epsilon. The aim was to build the tholos as ruins but at the same time give it a volume that refers to its height. The technique T used for building is the same as the one used to build the base but with lesser accuracy due to the fact that there is no reference to how the ring walls were built. However, corbelling stones were the main focus to show and prepare the model to look like a section in which the technique is visible.
Corbelling,Modeling, Sloping, Applying, Rendering.and
1 2 3 4 5
Ruin-like tholos Epsilon with three Minoan human figures showing the scale. Tholos Epsilon constructed of a stone base to a higher level with a wooden framework that supports the vault of lighter material.
The fifth option is actually challenging the cross-section adopted for the shape of the vault and pretends that in order to achieve a fully stone-built structure with the corbelling technique, the height of the tholos should correspond to the large diameter (9 meters), the thickness of the walls, as well as the gradual inclination resulting from the offset of the stones inwards. Applying this to a curvature that follows the orientation of the slightly inclined walls, gives the height seen in the fifth proposal bearing in mind the opening in the top of the tholos that was, hypothetically, used to fumigate the space after the burn of the deceased bodies. Tholos Epsilon with a flat roof of wooden beams, rubble, and a layer of soil.
Tholos Epsilon with stone base up to a high level followed by lighter material covering with the support of a central pillar.
Key Elements of the
Model.
Tholos Epsilon Flat Roof.
Tholos Epsilon with a flat roof of wooden beams, rubble, and a layer of soil.
Tholos Epsilon with stone base up to a high level followed by lighter material covering with the support of a central pillar. Wooden Pillar.
Tholos Epsilon Vault and central
EpsilonTholos Vault and Structure.Wooden
Tholos Epsilon constructed of a stone base to a higher level with a wooden framework that supports the vault of lighter material.
Work of: Talah talah.alshami@gmail.comAlshami Supervisor: Prof. Diamantis diamantis.panagiotopoulos@zaw.uni-heidelberg.dePanagiotopoulosArchitectureLandscapeArchaeologyErasmus+JointMaster’sDegreeALA2021-2022NationalTechnicalUniversityofAthensLaSapienzaUniversityofRomeCoimbraUniversityMarch-June2022
