The church of Agios Petros is the oldest of the ten byzantine monuments of Megali Kastania in Mani. It is the most important example of the so-called Helladic school of byzantine architecture in Messenian Mani. It is Tthe simple, domed, four-column cross-in-square church. Built with cloisonné masonry, it dates to the third quarter of the 12th cent. A stoa-shaped narthex was added at the west of the church in the 13th century. The impressive three-storey bell tower was built, according to an inscription, in 1813. Particularly interesting is the church’s sculpture, which survives almost intact; it comprises the capitals of the four columns, the frame of the west entrance and the iconostasis. These are works of impressive style and repertoire and have been attributed to one of the leading marble carving workshops of the 12th cent.

Three phases of wall paintings can be traced. The first two date to the byzantine period, while a third, post byzantine, one can be seen in the apse of the prothesis. The second layer is more extensively preserved, being the main decorative phase of the church. It is dated to the second half of the 14th century and echoes the trends of monumental painting in the region of Mystras during the late palaiologian period. Three byzantine wall painting layers have also come to light in the narthex during recent conservation work.