was converted to a mosque

 It was used as a mosque for a while during the reign of the Ottomans. There's traces of that past still visible. The writing says, ' and that the mosques are Allah's therefore call not upon any one with Allah.' It was written that these Moslems were very tolerant and recognised fine art, they didn't scrape off the frescoes but merely paint over them with whitewash to cover them and therefore preserving them for posterity.