The history of the Church of the Transfiguration of the Saviour - also knowns as Frankoklisia - probably began during the time of the Frankish occupation of Nafplio, when the church must have been used as a convent for Franciscan nuns. Shortly before the outbreak of the Greek revolutionin 1821, when Nafplio was still under Turkish control, the widow of the Aga-Pasha converted it into a mosque, as a memorial to her husband.

In 1839, with the mediation of King Otto (the first king of the modern Greek state), the Municipality of Nafplio granted the mosque to the Catholic Church, for the ecclesiastical needs of the approximately three hundred Greek and foreign Catholics - mainly the Bavarian soldiers who belonged to the king's entourage. After repairs, the church was officially opened in 1840.

The church has been in continuous operation from 1839 to the present day.