CONSTANTINOPLE – Some 86 years after being turned into a museum, the ancient venerable Orthodox Hagia Sophia cathedral in Constantinople on July 24 became a mosque again, as it did when the city fell to Turkish invaders in 1453.

Hundreds of Muslim faithfuls were making their way to the UNESCO World Heritage landmark to take part in the first official prayers for their religion since 1943, when Mustafa Kemal Ataturk, founder of modern, secular Turkey made it a museum.

The structure has been renamed The Grand Hagia Sophia Mosque, a contradiction in terms, keeping the word “Saint” in its name.

Turkish President Recep Tayyip Erdogan, who ordered the conversation to pacify his hard-core religious base – Turkey's highest court deferred to him, indicating he is the law – was scheduled to attend the inaugural prayers inside the 6th Century monument along with around 500 dignitaries, as he fulfills what he has described as the “dream of our youth” anchored in Turkey's Islamic movement.

Thousands of men and women, including many who traveled from across Turkey, are set to perform prayers in segregated areas outside Hagia Sophia. Several camped near the structure overnight.

Orthodox church leaders in Greece and the United States, meanwhile, were scheduled to observe “a day of mourning” over the inaugural prayers and with Greece trying to find a response after the church doors were already closed to Christianity.

Ignoring international pleas not to change the status of the cathedral, Erdogan issued a decree for the conversion after the judiciary he essentially controls after purging the courts following a failed 2016 coup against him said it had unlawfully been changed into a museum by Ataturk, a revered historic figure to most Turks.

The move sparked dismay in Greece, the United States and among Christian churches who had called on Erdogan to maintain it as a museum as a nod to Istanbul's multi-religious heritage and the structure's status as a symbol of Christian and Muslim unity. Pope Francis expressed his sadness.

Hagia Sophia, renowned as one of the world's most beautiful buildings, was built by the  Byzantine Emperor Justinian in 537, draws more than 3.3 million visitors a year, who had paid an entrance fee, now waived with the conversion to a mosque.

Although an annex to the Hagia Sophia, the Sultan’s Pavilion, has been open to prayers since the 1990's, religious and nationalists group in Turkey have long yearned for the nearly 1,500-year-old edifice, which they regard as the legacy of Ottoman Sultan Mehmet the conquerer, to be reverted into a mosque.

“This is Hagia Sophia breaking away from its captivity chains. It was the greatest dream of our youth,” Erdogan said “It was the yearning of our people and it has been accomplished.” Erdogan also described its conversion into a museum by the Republic’s founding leaders as a mistake that is being rectified.

In New York, the Greek Orthodox Archdiocese of America, called the inaugural prayers a “cultural and spiritual misappropriation and a violation of all standards of religious harmony and mutual respect.” It called on the faithful to observe a day "of mourning and of manifest grief,” over the change.

(Material from the Associated Press was used in this report)