It's a ruin of an ancient greek city. Apollonia was founded in 588 BC by Greek colonists from Corfu and Corinth, on a site where native Illyrian tribes lived, and was perhaps the most important of the several classical towns known as Apollonia. Apollonia flourished in the Roman period and was home to a renowned school of philosophy, but began to decline in the 3rd century AD when its harbor started silting up as a result of an earthquake. It was abandoned by the end of Late Antiquity.
More of this place tomorrow... :-)
Steepshot