The site of Ancient Halassarna is located in the modern village of Kardamena on the south coast of Kos, approximately 30 kilometres southwest of the capital city. Neolithic, geometric and classical remains unearthed in systematic excavations by the University of Athens over the past 30 years reveal the continuity of settlement in the ancient city, which flourished in Hellenistic times and retained its vitality throughout the Roman and early Christian periods. Combined with rich finds, the settlement, the cemetery and four Early Christian basilicas reveal a thriving city with workshops, small industry installations and significant commercial activity.

The Basilica of the Holy Godhead was identified and excavated by German archaeologist Rudolf Herzog in the early 20th century. It is a three-aisled basilica of impressive dimensions (60m in length) with a narthex , an atrium and a three-sided sanctuary apse. The church floors are meticulously decorated with mosaics, and ancient materials (marble architectural members and inscribed columns) are incorporated into the walls. The monument was built in the 5th century.

A second important basilica was recently discovered in the centre of the modern village of Kardamena. According to inscriptions, the founders were Dorotheus, Eutychius and Photeinos the Senior. Measuring 27 by 14 metres, it was erected around 500 and remained in use until the mid-7th century. This church is also a three-nave basilica with narthex . The impressive picture afforded by the excavated ruins clearly shows the building’s basic features, such as a protruding central sanctuary apse; a rectangular atrium surrounded by galleries on three sides; a wing with six annexes along the north side of the church; and a rectangular baptistery with an apse and two baptismal fonts to the south-east, which is the only one of its kind on Kos. The floor mosaics were the product of a local workshop, and are mainly decorated in geometric patterns, featuring wheels, octagons, squares and crosses, with a few non-geometric bird and plant motifs.