The Church of Hagios Petros is situated in Mesogeia, in Kalyvia Thorikou, in the location known as Ennea Pyrgoi (Nine Towers). It is 40 km southeast of the center of Athens. Both the architectural type and the use of stone between the windows date the church between the end of the 12th and the beginning of the 13th century. It is a two-columned, cross-in-square church with dimensions of 9,82 x 6,88. Many fragments of older buildings and tombstones have been incorporated into its rubble masonry. The wall paintings are of the same era.
A portrait of Michael Choniates, bishop of Athens, in a halo is found in the altar. In the north arch of the cross one can detect the wall paintings of Hagios Mamas and Hagios Triphon, saints associated with agrarian production, cattle-breeding and viniculture, a fact justified by the agrarian character of Mesogeia. According to the donator’s inscription in the narthex, a group of artists decorated the church. The sanctified portrait of Michael Choniates confirms a type of folk worship undoubtedly connected with the bishop’s activities and spiritual personality.