Church of Osios David Thessaloniki

This serene little 5th-century church, once the katholikon (major church) of the Monastery of Saviour Christ of Latomos, is one of the most significant early-Christian sites in Thessaloniki. It contains rare 12th-century frescoes and an even-more extraordinary 5th-century mosaic of Christ and the prophets Ezekiel and Habakkuk. Utterly glorious, it was covered up by the Turks during the church's time as a mosque, and only rediscovered in 1920.