The 1,500-year-old Hagia Sophia in Istanbul, Turkey, will become an active mosque beginning on July 24, ending its 85-year run as a secular museum.

Byzantine Emperor Justinian I ordered the building’s construction in 532 CE; for nearly 1,000 years, its 55.6 meter (180 ft) dome covered the largest indoor space in the world. Over a millennium and a half, the monumental structure has been an Eastern Orthodox cathedral, a Roman Catholic cathedral, an Eastern Orthodox cathedral again, and then a mosque.

Today, the Hagia Sophia is one of Turkey’s largest tourist attractions; an estimated 3.7 million people visited the site in 2019. It became a museum in 1934, under a decree from the Cabinet of Ministers under then-president of the Turkish Republic, Mustafa Kemal Ataturk.