In between Sagkri and Agiassos, on a cliff, stand the dominating ruins of a Byzantine castle with a great history and great importance to the island. Apaliros Castle was a defensive bastion against pirate raids and the centre of a lively and significant settlement with a relatively large population, during the Byzantine period.
Although there are no sources which mention the foundation of the city, it is certain that it was abandoned in the 13th century, when the Venetians came to the island. According to the tradition, Markos Sanoudos, determined to conquer the castle (which at the time was in the hands of the Genovese pirates) and to occupy the island, burned all his ships, forcing the soldiers to fight to the end.
Today, here you can see a large part of the walls, with towers and bastions, the two-aisled temple of Agios Georgios, many cisterns and the remains of about 250 homes, churches, bakeries and olive mills. You reach it via a walkable trail that starts about 500 meters from the information sign on the road from Sagkri to Agiassos.