The present day ruins of the Kastro are of a fortified area built on top of the ruins of the acropolis (high point) of Patras. The Kastro roughly triangular-shaped Kastro protected about five and a half acres (22,000 sq.m.) of land, and was strengthened at different points with watchtowers, gates, and a moat. There was also a moat-protected inner compound in one corner of the triangle. It was built after a major earthquake in 551AD by the Byzantine Emperor Justinian I, a ruler of some consequence who expended a lot of energy trying to reclaim the western half of the empire, which had fallen to the Germanic leader Odoacer in 476.
A lot of building material was recycled from previous, pre-Christian construction on the site. During construction, the torso of a woman with the bearded head of a man affixed to it was discovered. They were probably parts of two different statues. Some think the head is that of Zeus, or of Patreas, founder of Patras. She is known as the "Patrinella," and is supposed to protect the city against pestilence. She is said to weep every time someone important in Patras dies. She has been set in a niche in a tower in the southern wall of the Kastro. She is also known as The Ghost of the Castle.
The Kastro has its own museum featuring artifacts from the site, and a 700-seat theatre which is used to hold concerts and theatrical performances. Despite attempts by many invaders, the walls of the Kastro have never been breached. It was in use continually as a defensive fortification from the time of its construction until the end of WWII.
