The Aghios Ioannis basilica in Mastichari is situated at the end of the beachfront walkway, at a distance of about 60m from the sea, like most early Christian basilicas in the wider region during the 5th and 6th century AD, as it was a period devoid of danger from pirate raids. The basilica was built between the earthquakes of 469 and 554 AD, maybe on the location of a Temple of Hera. The basilica was long thought to be a church dedicated to St. John and the surrounding area surrounding was populated until the end of the 19th century but was then abandoned. A lot of stones and remains were used to build other churches in the region. In 1947 the architect Anastasios Orlandos started a systematic excavation of the site, uncovering the architectural, sculptural and artistic marvels, some of which you can explore to this day. The side aisles and the southern structures were dug up in 1955.
The basilica is 19.90×16.60 m (30.3×27.7 m in total) and follows Eastern and African patterns. It doesn’t have an atrium, like all basilicas in Kos except for those in Aghios Stefanos. It is a tripartite hellenistic basilica, with the narthex attached to the west and the large semicircular apse of the altar to the east. The baptistry, with a vestibule, is attached to the NE corner of the church, while a three-part structure of the diaconal compartment adjoins the entire south side. The synthronon and 4 rests of the ciborium (altar table cover) were found in the altar that was pillaged. 9 pillars of the inside colonnades of the church, with sculpted crosses and Ionic capitals with figures, rested on pedestals taken from Roman buildings. A number of ancient columns and artifacts were used as building material and adorn the sides of the structure. Pieces of small square pillars and carved parapets from the marble iconostasis of the basilica were also found. Two wash-basins were uncovered, to the right and left of the door that led from the narthex (14.5×4.65 m) to the main church.The staircase leading to the place intended only for women (gynaikonitis) is also visible.The baptistry of the Aghios Ioannis basilica consists of two chambers, a special vestibule and the main area, with a cross-shaped font. It is square-shaped externally but forms an octagon internally, with 4 semicircular niches and a fifth to the east for the Bishop. It had a hemispherical built roof, whereas the basilica had a wooden one. The baptism was most probably performed by sprinkling or pouring water in white clay jugs, like those that were found in the SE niche of the baptistry. Remnants of multicoloured murals with patterns imitating inlaid marble decorations can still be seen.A number of wonderful mosaics decorate the floors, covering a surface of about 400 square meters, but are currently, for the most part, covered by rubble, to protect them from the weather and decay, so you will only be able to admire the few uncovered parts. With the exception of the baptistry’s vestibule and the chamber of the southern adjacent structure, all floors of the basilica were covered with multicoloured mosaic representations of geometric designs (especially “Syrian wheels” i.e. larger circles joined with smaller cyclical bands), birds, flowers, fruits, vases and eight votive inscriptions in total. The materials used were local marble and limestone, tile and artificial coloured glass mass. Fine sheets of silver were used to cover the tessera of the necks of birds and sheets of gold to cover those of the baptistry’s luxurious inscription.