Greek archaeologists are calling on Unesco to protect the Hagia Sophia, the religious and cultural site in Istanbul, Turkey, that’s nearly 1,500 years old.

The Hagia Sophia, one of Turkey’s most popular tourist sites, has been a Unesco World Heritage Site since 1985. However, in recent years, the Byzantine-era building has suffered increased vandalism and damage. Writing in an open letter to Unesco’s director general, Audrey Azoulay, last week, members of the Association of Greek Archaeologists asked the organization to “intervene forcefully to reverse the current situation.”

In July 2020, a Turkish high court stripped the Hagia Sophia of its museum status, allowing it to be used as a functioning mosque. In recent years, the archaeologists claim, the historic site’s managers have allowed an “uncontrolled flow of visitors” to enter the building unchecked, without regard for the facility’s artistic and historical significance.

“The Ottoman wooden door leaves of the Imperial Gate were damaged, wall coatings were scraped and removed, fountains and doors were used for shoe storage, marble floor slabs were destroyed,” the archaeologists write in the letter. “The unique Byzantine mosaics remain covered and unseen. Archaeological supervision has stayed outside the monument.”

The letter references a handful of incidents that made headlines following the 2020 court decision. Earlier this summer, heavy cleaning equipment cracked the Hagia Sophia’s marble floors. And before that, in April, a group of Turkish art historians tweeted a photo showing damage to the building’s 23-foot Imperial Gate.

Unless someone intervenes, the archaeologists see “gloomy prospects” ahead for the Hagia Sophia, they write in the letter.

Constructed between 532 and 537 C.E. under the direction of Justinian I, the building served as a Christian cathedral—the largest in the world—for more than 900 years. In 1453, when the Ottoman Empire captured Constantinople, the site became a mosque. Later, in 1935, Turkish leader Mustafa Kemal Atatürk designated it as a museum.

The push to take away the Hagia Sophia’s museum status started in 2005, when advocates petitioned the country’s high administrative court. The court ultimately agreed with the petitioners, opening the Hagia Sophia to worshippers and handing over the site’s management from Turkey’s Ministry of Culture to the nation’s religious affairs department.

At the time of the decision, Unesco issued a statement saying it deeply regretted the decision to change the Hagia Sophia’s status. As Kristin Romey wrote for National Geographic in 2020, any attempt to modify a World Heritage Site requires prior notification of Unesco, as well as a review by the World Heritage Committee.

“Hagia Sophia is an architectural masterpiece and a unique testimony to interactions between Europe and Asia over the centuries,” said Azoulay in Unesco’s 2020 statement. “Its status as a museum reflects the universal nature of its heritage, and makes it a powerful symbol for dialogue.”

But even before the 2020 ruling, conservationists were worried about the fate of the Hagia Sophia, which struggled to get consistent funding for preservation work. It’s also situated atop a fault line, so an earthquake or tremor could cause serious damage to the site. As John Stubbs, a longtime advisor to the World Monuments Fund, told Smithsonian magazine’s Fergus M. Bordewich in 2008, the Hagia Sophia is an “unbelievably complex structure.”

“There’s the roof, the stonework, marble, mosaics, paintings,” Stubbs said. “We don’t even know all that’s in play in there. But we do know that it requires ongoing, vigilant attention. Hagia Sophia is an utterly unique building—a key monument in the history of architecture and a key symbol of the city of Constantinople right through to our time.”