The ruins of an impressively large Early Christian basilica known as the Basilica of Lechaion lie on a sandy spit of land by the ancient port of the same name. It is believed to have been built on the shore to honour Leonides, Bishop of Athens, and the seven women who were martyred with him in Corinth in the 3rd century, and whose bodies washed up on Lechaion beach.

Measuring 180 metres in length, the building is one of the largest basilicas in the Christian world, alongside the original St. Peter's Basilica in Rome. It is a three-aisled basilica with a transverse five-part aisle, semicircular apse, five-part narthex , and two atria surrounded by a portico, one of which is rectangular and the other semicircular. There were tribunes over the narthex and the aisles. In the northwest corner of the basilica there is a tripartite baptistery , in the form of an independent complex reminiscent of contemporary baths. It is probably older than the basilica.

The nave was divided into three aisles by two rows of columns, with a synthronon in the semicircular apse. Parts of the templon supports were unearthed at the point where the solea began. This ended in an octagonal pulpit with two staircases in the middle of the centre aisle. The basilica floors were covered with opus sectile and white marble slabs; the abundant high quality Proconnesian marble sculpture decoration is probably evidence of an imperial donation.

A coin from the reign of Emperor Marcian (450-457 AD) unearthed in the church floor foundations indicates that building work on the basilica commenced after the mid-fifth century. Similarly, a Justin I coin (518-527 AD) from the foundations of the west narthex shows that the church was probably further extended in the first quarter of the sixth century.