The acropolis of Serres crowns a low hill on the northern edge of the modern city. The Byzantines fortified the site from the sixth century onwards, and most of what is visible today -- the curtain wall, the gates, and the surviving tower -- dates from the late Byzantine period. The five-storey tower of Orestis is the most prominent surviving structure, a square keep of dressed stone and brick courses, built around 1350.
The climb up is steep but short, and the view from the top takes in the whole city, the broad plain to the south, and on a clear day the snowfields of Mount Pangaio. The ruins are unfenced and free to visit at any hour. There are no facilities at the top; bring water in summer.