Situated southern of Nea Anchialos, outside of the ancient walls. The excavations took place in 1971, 1978 and 1979.

It is a three-nave basilica with vestibule, built on the ruins of an ancient buildings (probably dated the 4th century a.C.). The archaeological pickax brought into light the base of the Holly table of the sanctuary and the «synthronon».

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The eight sided columns of the presbytery are very characteristic. The floors of the northern part of the building as well as the vestibule are covered with mosaics, rich in texture and theme.​

The basilica took its name «Martyrion» from an epigraph found at the beast of the presbytery, dated the 431 a.C.