There are two churches on the 3.5 acre complex of Hosios Loukas Monastery. The earliest was the Church of the Theotokos (Virgin Mary), built in the mid-10th century. The second – this domed cathedral called Katholicon – was finished in 1012. The middle-Byzantine façade features pairs of arched windows separated by marble mullions. The walls are a combination of brick, marble and stone. This type of Roman masonry is called opus mixtum. The interior is filled with Macedonian Renaissance frescos and mosaics with gold backgrounds. They are the best examples in Greece of this style of Christian artwork from the 10th and early 11th century. You will admire more frescos in the crypt were Saint John is buried.