Restoration of Hagia Sophia Kebîr Mosque

Hagia Sophia, which was converted into a mosque with the conquest and served as a mosque for 481 years, was closed to the public with the start of restoration works in the 1930s. It was then converted into a museum with a Council of Ministers decision dated 24 November 1934. The Council of State cancelled the decision of the Council of Ministers on 10 July 2020. Immediately afterwards, Hagia Sophia was reopened to worship with the Presidential Decree No. 2729 issued with the signature of President Recep Tayyip Erdoğan.

Hagia Sophia Kebir Mosque is one of the oldest surviving buildings in the world for 1486 years. During this time, it has been exposed to many disasters, especially earthquakes, partial collapse-collapse and fires. In the 570 years since the conquest of Istanbul by Mehmed the Conqueror, extensive fortifications, repairs and restorations have been carried out to keep Hagia Sophia alive, and it has turned into a complex with structures such as imaret, madrasah and tombs added around it in time. Today, Hagia Sophia is carefully protected and kept alive. In this context, under the supervision of the General Directorate of Foundations, the Istanbul Directorate of Survey and Monuments and the Governorship of Istanbul, the restoration of the Mausoleums, the SıbyanSchool and the Muvakkithâne has started with holistic project works.

Preparation of Comprehensive Projects


  1. Documenting all the buildings in the complex together with their immediate surroundings in three dimensions with all their details and leaving them as a legacy for future generations,
  2. In particular, to determine the structural condition of the Hagia Sophia Kebir Mosque, to examine its possible behaviour in the face of a possible major earthquake, and to take measures to ensure the survival of the building,
  3. Bringing together, classifying and digitising the information, documents and projects in the archives and academic literature from the past to the present.
Scope :

The works carried out within the scope of the preparation of holistic projects are as follows:

  1. Information Document Management
  2. Three Dimensional Measurement and Evaluation
  3. Building Radar Construction
  4. Preparation of Survey and Analytical Surveys
  5. Making Period Analyses
  6. Determination of Earthquake Safety (Structural Modelling and Static Performance Analyses)
  7. Preparation of Restoration Projects, Determination of Intervention Methods

1.Information Document Management

It is known that many institutions have carried out various studies, projects and restorations related to the Hagia Sophia Kebir Mosque complex over time. It is obvious that information-document management is of great importance for future studies, applications, researches and scientific publications. For a holistic approach, it is necessary to bring together all the works carried out from the past to the present and to archive and classify them digitally using technological means. Individual archives, archives of foreign universities, academic literature, etc. are also scanned and studies, documents and visuals related to Hagia Sophia are transferred to the digital environment.

2.Three Dimensional Measurement and Evaluation

A holistic, high resolution, detailed point cloud data defined in the national coordinate system was created, covering all the buildings within the complex, the garden walls surrounding the parcel and the immediate surroundings of the complex. From this point cloud data, high resolution orthophotos were produced for surveys.

Within the scope of this study, state-of-the-art equipment and software were used and geomatics engineers experienced in three-dimensional surveying and evaluation were employed. Although three-dimensional laser scanning measurements were planned to be carried out, direction-edge measurements, satellite-based position determination and photogrammetric measurements were also needed in areas where necessary in order to establish a geodetic infrastructure and to control the measurements. In this respect, photogrammetry method, high resolution DSLR cameras and lenses were also used where necessary. Due to the size of the structure, photogrammetric completion was carried out using drones. The accuracy of the measurement was increased by creating ground control points for photogrammetric measurements.

It is aimed to have an up-to-date digital twin of the building by continuously updating this point cloud, which is high resolution and reflects the real geometry and architectural features of the building, in future studies.

3. Building Radar Construction

Considering that the structure of the Hagia Sophia Kebir Mosque is approximately 1500 years old, structural radar studies, which is a non-destructive method, were carried out with academician geophysical engineers experienced in antiquities in order to investigate whether there are significant damages such as mortar discharges, subsequent cavities, cracks, crevices, dampness, etc. in the structural elements and whether there are structural elements (such as beams, tensioners) that cannot be seen from the outside.

4. Preparation of Survey and Analytical Surveys

Survey and identification studies consisting of two-dimensional drawings documenting the current condition of the building are ongoing.

14 plans and (at least 8) sections and a sufficient number of detail projects are prepared.

Analytical survey studies are ongoing and material analysis and damage-disturbance analysis sheets are being prepared in this context.

5. Making Period Analyses

In its 1486 years of life, Hagia Sophia has suffered many earthquakes, large and small. It is known that the main dome was partially destroyed in the 6th, 10th and 14th centuries and that the destroyed parts were rebuilt, and that it underwent continuous repairs both in the Eastern Roman, Ottoman Empire and Republican periods. It is aimed to determine these repairs as much as possible through period analyses.

6. Determination of Earthquake Safety

The studies to determine the earthquake safety of Hagia Sophia and its minarets are being carried out under the supervision of Prof. Dr. Alper İlki, Faculty of Construction, Istanbul Technical University, and his team and the Scientific Committee.

A digital model of the structure is made using current point cloud data. Structural performance and earthquake behaviour analyses will be performed to determine possible damage and collapse modes. In analyses and investigations, the Guide for the Management of Earthquake Risks for Historic Buildings (2017) is used. Retrofitting proposals are developed, simulated and analysed on the model.

7. Preparation of Restoration Projects

After the survey, analytical survey, structural performance analyses and determination of earthquake safety, restoration projects will be started to be prepared.

Currently approved restoration projects prepared by different authors are as follows:

  • ”Hagia Sophia Kebir Mosque-Sharif North, South and East Facades Restoration Intervention Projects”: It was prepared under the supervision of the Istanbul Governorship Investment Monitoring and Coordination Presidency and the Ministry of Culture and Tourism and was submitted to the Istanbul Regional Board for the Protection of Cultural Assets No. IV with the approval of the Hagia Sophia Scientific Board and approved by the board’s decision dated 04.08.2021 and numbered 8215.
  • ”Hagia Sophia Minarets Restoration Intervention Projects”: It was prepared under the supervision of the Istanbul Governorship Investment Monitoring and Coordination Directorate and the Ministry of Culture and Tourism and submitted to the Istanbul Regional Board for the Protection of Cultural Assets No. IV with the approval of the Hagia Sophia Scientific Committee and approved by the decision of the board dated 08.03.2023 and numbered 11191.
In line with these approved projects and with the recommendation of the Hagia Sophia Scientific Committee dated 19.01.2023, comprehensive restoration works will be started. Restoration works will be carried out in stages.

8. Ongoing Restoration Works

Located in the complex;

  • MAUSOLEUM OF SULTAN MEHMED III; The upper cover was renewed, the existing dome was removed and rehabilitated. Gold leaf application was made on the entire surface. Fine mechanical and chemical cleaning was performed on the exterior marble coating surfaces. Surface losses on the embroidered and profiled eaves marbles were repaired and integrated. Marble facade claddings and facade columns were reinforced with injection and stitching in hairline cracks. Necessary maintenance and repair works were carried out on iron railings with sockets, wooden doors with tables, bronze railings, wooden wings with kündekari tables, interior and exterior doors. Restoration works are ongoing.

  • MAUSOLEUM OF SULTAN SELİM II; The upper cover was renewed. Repairs of structural deterioration in 8 arched dome windows were completed. The existing dome procession was dismantled and rehabilitated. Mechanical and delicate cleaning is being carried out on the exterior marble coating surfaces and restoration works are continuing.

  • MAUSOLEUM OF SULTAN MURAD II; Top cover renovation works have been started.

  • PRINCES TOMB: Top cover renovation works have been started.

  • TIMEKEEPING HOUSE: The built-in elements in the building (glass partition, screen entrance and similar) were dismantled. The falsified wooden floor covering was dismantled. The plasters deteriorated by exposure to moisture and the later cement plasters were scraped. Joints were opened on plaster rubbed surfaces. Re-grouting was carried out on the grouted surfaces and rough and thin plasters were applied. Careful surface cleaning was carried out on the marble columns. The paint layer on the plaster relief decorations on the ceiling, walls and lanterns was carefully scraped. The oil paint on the wooden door was carefully scraped. Careful paint scraping was completed on the wooden window joinery. The paint layer consisting of several layers on the original plaster was carefully scraped. The paint layer on the ceiling plaster was scraped.  Window marble surfaces were cleaned. The original wall plaster surfaces that needed to be protected were reinforced with microinjection method. The missing motifs of the plaster ornaments on the interior walls were reproduced according to the template and the missing parts were completed. Restoration works are ongoing.

  • SIBYAN SCHOOL: Cement mortar plasters on all interior walls, vaults and domes were scraped. The later cement mortared unqualified fillings that emerged after the plaster scraping on the wall faces were removed and wall coverings were made in details suitable for the existing original masonry. The invalid elements were removed from the building. Restoration works are ongoing.

  • SIDE DOOR:  Marble and stone surfaces were cleaned precisely. Marble cleaning was carried out on profile carved surfaces. The top cover was renewed. The marble realm was removed from its place. The surface was cleaned and reassembled. Restoration works are in progress.

  • FRONT OF MEYYIT ROOM (EXTERIOR): Research excavation was carried out. Projects were prepared according to the situation that emerged as a result of the research excavation.