Five things to know about the Hagia Sophia

A top Turkish court ruled on Friday that the Byzantine-era Hagia Sophia, which has served as a museum in Istanbul since 1935, would be handed over to Turkey's religious affairs directorate and reopened for Muslim worship.

Here are five things to know about the Hagia Sophia:

The edifice was first built as an Orthodox Christian church between 532 and 537 AD under emperor Justinian I and is considered the most important Byzantine structure.

After the Ottoman conquest of Constantinople (now Istanbul) in 1453, it was converted into a mosque before being opened as a museum in 1935 after the secular modern Turkish republic was established in 1923.

It was added to the list of UNESCO world heritage sites in 1985.

Following Friday's decision, it reverts from being a museum to being a mosque.

The Council of State, Turkey's highest administrative court, unanimously cancelled a 1934 cabinet decision and said Hagia Sophia was registered as a mosque in its property deeds.

Until now it has been the principal tourist attraction in Turkey, hosting millions of tourists every year -- 3.8 million visitors in 2019.

There has been more religious activity inside the museum in recent years -- Turkish President Recep Tayyip Erdogan recited the first verse of the Koran in 2018.

Tourists could still visit the Hagia Sophia, just as they are able to see the Blue Mosque nearby.

But the example of the Hagia Sophia of Trabzon in northern Turkey, opened to Muslim worship in 2013, may give pause for thought.

"The number of visitors dropped significantly following its transformation into a mosque, especially because visitors could no longer appreciate the church's famous frescoes," said Tugba Tanyeri Erdemir, a research associate at the University of Pittsburgh, adding this had a negative impact on locals who depend on tourism revenues.

There was a long legal process leading up to Friday's ruling.

The Constitutional Court in September 2018 turned down a plea by an independent heritage association to open the building up for Muslim worshipping.

The main opposition secular Republican People's Party (CHP) has accused the government of using the issue to distract voters from economic woes and other issues following the coronavirus pandemic.

"Erdogan appears to be responding to a drop in voter support, which is likely a fallout from Turkey's COVID-19-induced economic downturn," said Erdemir.

Erdogan's supporters praised him for getting involved with lavish celebrations for the anniversary this year of the 1453 conquest of Constantinople, encouraging him to be more proactive, said Erdemir.

As early as 1994 when he was running for mayor of Istanbul, Erdogan promised to open the building to Muslim worshippers.

The landmark ruling has already inflamed tensions not just with the West and Turkey's historic foe Greece, but also Russia, with which Erdogan has forged an increasingly close partnership in recent years.

Turkey-Greece relations are already strained over migration and drilling in the eastern Mediterranean.

Greece branded the move an "open provocation to the civilised world", while the Russian Orthodox Church said Turkey had ignored "millions of Christians" with its move.

The United States had also urged against altering its status.

The UN's cultural agency UNESCO earlier Friday warned Turkey against converting Hagia Sophia into a mosque, urging dialogue before any decision was taken.