Conservation of the city walls of Istanbul
The land wall of Constantinople, a strong fortification from the reign of Theodosus II (406-450 AD), marks the western border of the ancient city. The strategical life of the wall lasted about a thousand years, during which period it suffered from serious tremors and had to be repaired several times. Today, even in their ruinous state, the wall sections and towers bear testimony to the grandeur of the fifth century military architecture. Conceived as the most developed defense system of the ancient world, Theodosian walls consist of three members: the inner wall with rectangular or polygonal towers, the outer wall with rectangular or U shaped towers and the moat.
In october 1991, a team of architects and engineers from Istanbul Technical University started to work on a 250 meters long portion of this structure. The site under consideration was the southern end of the seven kilometer long land wall; strating with the first tower (T1) and ending at a point to the north of the sixth tower (T6). Originally T1 was connected to the sea walls by a curtain wall, the remains of which were removed during the construction of the moktorway in late 1950. The intercity railway which was introduced in 1870’s piercing through the section of the wall between Tower 6 and 7, demarcates the boundary of the project area towards the north.
The main wall was relatively well preserved between T1 and T6, but the outer wall and the moat were only perceptible above ground, due to changes in the topography and the damages caused by the crouching of industry since the end of the last century. The occupation of the area by tanneries lasted until 1990, when the Municipality of Istanbul finally succeeded in the clearing. Clearance in the project area brought to light the 250 m long section of the wall which was completely curtained by tanneries. The first three towers of the outer wall had diappeared completely, leaving no vestige above ground level. The wall surfaces had been stained with dyes or chemicals used in leather industry; there were several cavities and flues dug into the wall mass. A thick layer of earth was deposited above the rampart walk and towers, providing firm ground to several fully grown trees. The vegetation and the earth deposit had to be removed with care. On the eastern side of the wall, access to the towers was hardly possible, due to accumulation of about three meters high debris, which changed the ground level along the walls. Excavation was conducted until the original ground and floor levels were reached. For complete documentation and understanding of the structure excavation continued within the towers, revealing interesting details about the history of the structure.
The second step in the work was preparing surveys which provided the basis for further investigation on the wall, such as the analysis of different phases of construction and structural problems. They also provided the principal documents on which the result on the inspection of the present fabric were recorded, leading to decisions for conversation measures. Photogrammetry was employed for elevations. Professor Cankut Ömerci and associate Professor Oðuz Müftüoglu from the Photogrammetry Department of Istanbul Technical University were produced by a team of architects specialized in conservation. The ruinous state of the walls and towers presents a complexity which required a combination of geodesic and direct measuring systems.
The first tower had been restored in 1988, along with the western elevation of the curtain wall connecting it to the second tower. This was part of a larger restoration project covering two of the city gates.
From the start, we planned to limit interventions to a minimum. Our objective was to strengthen the existing fabric, so that it would suffer less from climatic factors and also resist future earthquakes. We preferred to use materials which would match the originals. This required research of the mortars, brick sizes and types of stones used in the original as well as the historic repair phases. Due to earthquakes and ravages of time, the wall had to be repaired several times, using different mortar mixes, brick sizes, and stones. Conservation of the historic sequence of these repairs also posed problems which had to be tackled with care. The composition of mixes of mortars were developed by laboratory research. In the fifth century mortar, pozzolanic property was provided by the brick dust. For medieval repairs, lime mortar with coarse sand and crush brick had been used. A new mix was prepared with matching color and composition to be used for repointing these sections.
Actual work on the wall started beginning of February 1992 by the consolidation of the section between T1 and T2. The eastern façade had been restored in 1988. Due to the presence of tanneries on the site, the western side was only partially treated. Work continued until end of 1993. With the change in the local government, the work could not continue after the elections in 1994. During the two and a half years of our study we were able to prepare the restoration drawings for the second, third and fourth towers. The wall section was treated until the fifth tower but it was not possible to restore Tower 4. Although the documentation was completed, we did not have the chance to consolidate and restore the outer wall or excavate the moat in this part of the wall. We hope there will be better times and it will be possible to continue research and excavation.Historical analysis, conservation design and supervision: Metin Ahunbay and Zeynep Ahunbay.
Structural analysis and design: Müfit Yorulmaz and Feridun Cili.
Material Science: Nihat Toydemir and Erol Gürdal.
* Pour plus de détails sur la restauration des murailles, voir l’article du même auteur dans la Lettre d’Information de l’Observatoire Urbain, nº 7, décembre 1994.