Turkish President Tayyip Erdogan declared Istanbul’s Hagia Sophia a mosque on Friday with the first Muslim prayers to begin in two weeks, after a top court ruled the ancient building’s conversion to a museum by modern Turkey’s founding statesman was illegal.

Erdogan spoke on Friday just hours after the court ruling was published, brushing aside international warnings not to change the status of the nearly 1,500-year-old monument that is revered by Christians and Muslims alike.

The United States, Russia and church leaders were among those to express concern about changing the status of the UNESCO World Heritage Site, a focal point of both the Christian Byzantine and Muslim Ottoman empires and now one of the most visited monuments in Turkey.

“With this court ruling, and with the measures we took in line with the decision, Hagia Sophia became a mosque again, after 86 years, in the way Fatih the conqueror of Istanbul had wanted it to be,” Erdogan said in a national address.