Outside the Monolithos village is the medieval castle, built on top of a 100m rock. It was built in 1480 by the Knights of Saint John to protect the island from attacks. In fact, this castle was never conquered. The Castle of Monolithos is widely ruined today but it offers great views of the sea and the two islets opposite to it. Inside the castle, there is a small working chapel dedicated to Agios Panteleimon (Saint Pantaleon).
Access to the castle is by a staircase cut into the rock. The steps, whilst not particularly steep, are quite slippery simply due to the numbers of visitors wearing them away. On the climb up to the top, you are likely to see hundreds, if not thousands, of small piles of rocks from 3–10 in number. These piles are left there by the visitors as a form of a memento.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.