Hagia Sophia restoration turns to Edirne’s distinctive limestone

EDİRNE

Istanbul’s iconic Hagia Sophia is welcoming a piece of northwestern Türkiye into its ancient walls as ongoing restoration efforts introduce a distinctive limestone from Edirne to the monument for the first time in its history.

The küfeki limestone, sourced from quarries in the Süloğlu district, has long been used in major restoration projects across Türkiye, including the rehabilitation of the Selimiye Mosque and the revival of the historic Edirne Palace.

Conservation experts said the stone closely matches the physical and structural characteristics of the original material used in Hagia Sophia, making it the most suitable replacement for deteriorated sections.

Known for its unique properties, küfeki stone is relatively soft when freshly quarried, allowing craftsmen to shape it with ease. Once exposed to air, however, it gradually hardens through a natural chemical process, increasing in strength and durability over time.

This characteristic has made it one of the most valued building materials throughout the Roman, Byzantine and Ottoman periods, contributing to the longevity of many of the region’s monumental structures.

Speaking to Turkish state-run Anadolu Agency, Levent Çetin, a senior official from the Culture and Tou, said Istanbul’s monumental architectural heritage was largely constructed using locally sourced Bakırköy küfeki stone extracted from quarries once located around present-day Bakırköy, Bağcılar and Haznedar.

“Hagia Sophia itself was originally built using küfeki stone obtained from these quarries,” Çetin said. “However, due to the rapid urbanization of Istanbul over the decades, the historic quarry sites have disappeared beneath residential neighborhoods, making it virtually impossible to source the original material today.”

Conservation teams discovered that while much of the original Bakırköy stone remained intact, previous repair campaigns had introduced replacement stones brought from other regions.

“As dismantling work progressed, we identified stones from different geological sources that had been used during earlier interventions,” Çetin explained. “Technical assessments revealed that these replacement stones did not perform as well as the original Bakırköy limestone in terms of structural stability. This prompted us to search for a material that would be compatible both visually and mechanically.”

The search led specialists to the Süloğlu quarries in Edirne, where samples underwent comprehensive physical, mechanical and laboratory analyses before being submitted to the project’s scientific advisory board. Following the board’s approval and the completion of all necessary conservation procedures, procurement of the stone officially began.

Bedri Koza, owner of the quarry operating in Süloğlu, described supplying stone for one of the world’s most celebrated monuments as a source of immense pride.