On Tilos there are remains of several medieval castles, with the Knights Castle of Megalo Chorio standing out. It was built by the St. John Knights on the same spot where the ancient Acropolis stood, at the hillside. Inside you will come across the Archangel church which has a Gothic facade and was built in 14th-15th century on top of an ancient temple, while internally there are still preserved remarkable frescoes. Other medieval castles are that of Agiosykia with the ruins of the homonymous church and that of Messaria.