The establishment of the monastery Hosios Loukas was in 10 th century. The monastery was dedicated to the saint who lived near by the monastery. The monastery has two churches Panagia Theotokos and katholikon. Panagia Theotokos is smaller church, bui lt between the middle and the end of the century, while the construction of the katholikon can be assumed in the ye ar 1011 or 1022. Panagia Theotokos is a simple cross in square type, while katholikon is a modified cross in square type into octagon domed church. These two churches are the first of their type in the Greek territory and this is one of many reasons why th is monastery is so special. Hosios Loukas katholikon had an influence on other katholikons like Nea Moni and Daphne. Panagia Theotokos and the katholikon of Hosios Loukas except the similar church types, have their differences in size, number of domes and preserved decoration. Katholikon is much larger compared to Panagia and has two domes. Dome on octagon rises above squinches and is in the center of the church and the second dome is placed in the sanctuary on pendentives. The only dome in Panagia church r ises above four co l umns and pende t ives, while its exterior is octagonal. The preserved decoration inside the churches also varies. Panagia Theo to kos doesn’t have preserved frescoes or mosaics, but it has a sculptural decoration consisting of the capitals o f columns supporting the dome and a templon i n the interior. On the exterior the Panagia walls are decorated with pseudo k ufic ornament and clois o nne brickwork. The Hosios Loukas katholikon has the most significant mosaics of the Middle Byzantine period da ting from the 11 th century. Comparing the mosaics of the Hosios Loukas monastery with the mosaics of the Nea Moni and Daphne we notice that the mosaics of the Hosios Loukas are just the beginning of the development of style in the mosaic technique of that time.