Turkey’s plans to turn the ancient revered Greek Orthodox Churh of Aghia Sophia in Constantinople into a mosque has left Ecumenical Patriarch Vartholomaios unhappy and complaining it will further the division with Greece as tension soars between the countries.

“What can I say as a Christian clergyman and the Greek patriarch in Istanbul? Instead of uniting, a 1,500-year-old heritage is dividing us. I am saddened and shaken,” said Vatholomaios, who is spiritual leader of 300 million Orthodox Christians worldwide.

He was speaking to Turkish columnist Asli Aydintasbas for the Washington Post about the scheme that was hatched by Turkish President Recep Tayyip Erdogan, adding to provocations with Greece as he moves to have ships drill off Greek islands.

The seat of the Orthodox Church resides in the city still, 567 years after it fell to the Turks in 1453, marking the end of the Byzantine Empire, and effectively the end of the Roman Empire, a state which dated back to 27 BC and lasted nearly 1,500 years.

The 6th Century Christian cathedral was turned into a mosque after that but in 1935 the secular founder of modern Turkey, Kemal Ataturk – in power when Smyrna fell in 1922 – turned it into a museum, which has been since, becoming a popular tourist attraction, often drawing more than 3.5 million visitors annually.

The cathedral is a UNESCO World Heritage Site and draws visitors of all faiths for its majestic design, although Turkey has put minarets around outside.