The church is inside the actual cemetery, south of Kos town. The ground plan is circular with four semicircular corner conchs and one in the middle of the eastern side, inscribed within a quadrangle. Two more conchs in the middle of the south and north side, along with the five mentioned above, gave the church this name. Within, a concentric colonnade of eight smooth columns, has been partly replaced by walls. The entrance is in the middle of the west side of the church.

The church was originally an Early Christian baptistery of the 5th - 6th century, which belonged to a partly excavated basilica. No trace of the latter is visible today. This is perhaps the only Early Christian baptistery to have remained almost intact up to this day and is still in use as a cemetery church.

Frescoes of the 12th - 13th century, with scenes of the life of St. John the Precursor have been recently discovered, as well as others of the 16th century. The church' s masonry contains interesting elements, such as the reuse of a Hellenistic frieze with garlands on the lower part of the sanctuary apse, architraves, bases, Early Christian mullions, pilaster- capitals etc. in various parts of the walls.