Recep Tayyip Erdogan, the Turkish president, has signed a decree that will convert the 6th century Hagia Sophia into a mosque after the country’s highest court repealed the domed structure’s status as a secular museum.
First constructed as a Greek Orthodox Cathedral in 537 AD, the Hagia Sophia was turned into a mosque by the Ottoman Empire at the height of its power and then became a museum in 1934 on the orders of Mustafa Kemal Ataturk, Turkey’s founding father.
However, Turkish judges ruled on Friday afternoon that Ataturk’s cabinet decision to secularise the mosque and open its doors as a museum was illegal.
Shortly after the ruling, Mr Erdogan signed a decree which announced that the Hagia Sophia would reopen as a mosque, in defiance of pleas from Christian leaders and Unesco, which declared the structure a world heritage site in 1985.
Greece condemned the decision as “an open provocation to the civilised world,” while Russia’s Orthodox Church said it was bitterly disappointed and that “millions of Christians” had been ignored by Turkey.
The restoration of the building to its Ottoman-era status is a major political coup by Turkey's pugnacious leader, who has repeatedly vowed to turn the Hagia Sophia back into a mosque but faced intense pressure from the United States and other Western allies to abandon the plan.
"It was concluded that the settlement deed allocated it as a mosque and its use outside this character is not possible legally," the Council of State, Turkey's highest administrative court, said in its ruling.
"The cabinet decision in 1934 that ended its use as a mosque and defined it as a museum did not comply with laws," it added.
Orthodox Christian leaders spoke of their deep regret on Friday about the decision.
A spokesman for the Russian Orthodox Church said the ruling made clear that "calls for caution have not been heard."
Leonid Slutsky, chairman of the foreign affairs committee in Russian parliament, told the RIA Novosti news agencies that he was "sorry that the Turkish court canceled Kemal Ataturk's wise decision."
"There may be many mosques but Hagia Sophia is unique in its historic value,” he said.
In the eyes of the whole world Ankara is going to look like someone who has upset the inter-faith balance and is losing its authority as an important regional player," Konstantin Kosachyov, the influential chairman of the foreign affairs committee in the upper house of Russian parliament, said in his blog on Friday.
Russia, which has developed increasingly close ties to Turkey in recent years, kept silent on the plans to turn Hagia Sophia into a mosque until earlier this week when Patriarch Kirill, head of the Russian Orthodox Church, said he was "deeply concerned" by the move.
Lina Mendoni, the Greek culture minister, said in a statement that "the nationalism displayed by Erdogan... takes his country back six centuries."
The Hagia Sophia is considered one of the crowning achievements of the Byzantine era, but through Turkey’s turbulent history its ownership has shifted between Christianity and Islam.
The cathedral briefly became a Crusader church following its construction by Orthodox Christians but in 1453 was converted by the Ottoman Empire into a mosque.
The Ottomans added minarets alongside the domed structure, while inside they added calligraphic panels bearing the Arabic names of the early Muslim caliphs alongside the monument's ancient Christian iconography
Five hundred years later, Ataturk made the highly symbolic gesture of secularising a building claimed by both Christianity and Islam, as the country sought to recast itself as a pro-Western, secular power.