ISTANBUL - It has served as the exalted seat of two faiths since its vast dome and lustrous gold mosaics first levitated above Istanbul in the 6th Century: Christendom’s greatest cathedral for 900 years and one of Islam’s greatest mosques for another 500.

Today, the Hagia Sophia, or Ayasofya in Turkish, is officially a museum: Turkey’s most-visited monument, whose formally neutral status symbolises the secular nature of the modern Turkish state. But tens of thousands of Muslim worshippers gathering there on Saturday hope it will again be a mosque, a dream they believe Prime Minister Tayyip Erdogan can fulfil.

There are even rumours - denied by the government - that Erdogan, a religious conservative who is seeking the presidency at an election in August, could lead prayers there one day soon. ‘This is a serious push to break Ayasofya’s chains,’ said Salih Turan, head of the Anatolia Youth Association, which has collected 15 million signatures to petition for it to be turned back into a mosque. ‘Ayasofya is a symbol for the Islamic world and the symbol of Istanbul’s conquest. Without it, the conquest is incomplete, we have failed to honour Sultan Mehmet’s trust,’ he said, citing a 15th Century deed signed by the conquering Caliph and decrying as sin other uses of Hagia Sophia. Built in 537 by Byzantine Emperor Justinian whose rule stretched from Spain to the Middle East, Hagia Sophia - meaning ‘Divine Wisdom’ in Greek - was unrivalled in the Christian world until Ottoman Sultan Mehmet II conquered the city in 1453 and turned it into a mosque. Modern Turkey’s founder Mustafa Kemal Ataturk decreed it a museum in 1934.

Now, renewed interest in praying at Hagia Sophia taps into a burgeoning sense of Islamic identity that Erdogan has encouraged during a decade as Turkey’s dominant politician. For most of the 20th Century, Western-oriented Turks scorned the imperial past. But Erdogan has promoted celebration of the Turkish conquest that turned Constantinople into Istanbul.

‘Conquest is the removal of shackles on doors and in hearts,’ he said on Thursday to mark the 561st anniversary of the Byzantine defeat. ‘Civilisation comes with conquest.’ A 2012 film depicting the Muslim takeover of the Byzantine capital, ‘Conquest 1453’, attracted an audience of millions. So has the museum’s ‘Panorama 1453’ exhibition, which recreates the event in vivid detail.

Ibrahim Kalin, a senior Erdogan adviser, said there were no plans to alter the monument’s current status. ‘Speculation on changing it into a church or a mosque remains speculation. Hagia Sophia has been open to all visitors from Turkey and around the world and will remain so,’ he said. Last year, Erdogan said he would not consider changing Hagia Sophia’s status as long as another great Istanbul house of worship, the 17th Century Sultan Ahmed Mosque, remains mostly empty of worshippers. Istanbul boasts more than 3,000 mosques.

But many pious Turks believe turning Hagia Sophia into a museum denigrated the memory of Sultan Mehmet, who strode into the ransacked cathedral to pray at its altar. Calls for Hagia Sophia to be restored as a mosque have circulated before but were largely marginal until two years ago, when thousands of worshippers prayed at the monunment. Since then, Turkey’s chief mufti has recruited Istanbul’s most gifted muezzins to read the call to prayer from a sanctuary on its grounds, transmited through speakers on its brick-clad minaret.

The Koranic verses from Hagia Sophia create a soaring call and response with those read from across manicured gardens from the Sultan Ahmed Mosque. In what was widely taken as a hint, Deputy Prime Minister Bulent Arinc stood outside Hagia Sophia in November and said he ‘prayed to God it would soon be smiling again,’ then cited a law forbidding houses of worship to be used for other purposes.

A vigorous social-media campaign followed. This month, an independent lawmaker proposed a law to allow Muslim prayer. A pledge to make Hagia Sophia a mosque may draw some disaffected nationalist and religious voters back to Erdogan in the presidential vote after a year of anti-government protests and a corruption scandal, said Sahin Alpay, a professor of political science at Bahcesehir University and a columnist for the Zaman daily. But he argued it would not be worth the price.

‘It would strengthen the mutual suspicion and polarisation between the West and the Muslim world,’ Alpay said. ‘All hell breaking loose is a high price to pay.’ The U.S. Commission on International Religious Freedom, a bi-partisan advisory panel set up by Congress, said in a statement last week that such a move would threaten Turkey’s international standing and recall its mistreatment of Christians over the last century.