Explained: The battle over Turkey’s Hagia Sophia

Istanbul’s Hagia Sophia once divided Christians and Muslims, and that history may be repeating itself.

[Turkish historian Edhem Eldem, saying:] "What makes it unique is that it is more than a mosque, it is not just a mosque, it is also a basilica, a church. It has been for a thousand of years.”

There are many in Turkey who want to turn the World Heritage site back into a mosque, but it's a move that has prompted international outcry.

To understand the controversy, we need to go back, way back, to its origins in the sixth century.

It was completed in 537, built as a cathedral during the Byzantine empire.

Then the world’s largest church, it was the heart of Christendom.

And it stayed that way for around 900 years until Istanbul, then known as Constantinople, fell to the Ottoman Turks in 1453.

It was then converted into a mosque by the sultan, Mehmet the Conquerer.

The Ottomans added four minarets and covered Christian features with Islamic iconography.

Fast forward around 500 years and the transformation of Turkey into a modern secular republic.

The first president, Mustafa Kemal Ataturk, issued a decree making Hagia Sophia a museum in 1934, respecting both Christian and Muslim heritage.

Critics say overturning that decree is nothing more than a political move.

[Turkish historian Edhem Eldem, saying:] "The formula that was found in 1934 to appropriate it universally was to turn it to a museum and that was a political move. Now what we are seeing is yet another political move."

A Turkish association lobbied the courts for 15 years.

In the latest case, history itself was brought into the courtroom.

The group argued that Ataturk’s government did not have the right to overrule Sultan Mehmet’s wishes from 1453 - making the museum conversion unlawful.

The campaign was supported by President Tayip Erdogan, whose ruling AK Party sprang from political Islam.

Erdogan has put religion back at the heart of national life, chipping away at decades of secular dominance.

The mosque conversion certainly appeals to voters.

Many Turks argue it better reflects the country’s identity, which is overwhelmingly Muslim.

But internationally, the move has triggered outrage.

U.S. Secretary of State Mike Pompeo urged Turkey to maintain the neutral status of the site.

Greece and Orthodox leaders in Turkey and Russia warned it could sow division.

[Turkish historian Edhem Eldem, saying:] “The gambit here, the challenge is, where do you position yourself? Do you adopt a universalist vision and do you accept the idea that you can share a building with the entire world or do you want to claim it as yours?"

However for Erdogan, international criticism seems to represent an attack on Turkey’s own sovereignty.