The walls of the old town of Kos were built in a hurry between 1391 and 1396 in order to hold off the attacks of Bayezid I, who tried to conquer the island many times. A large part of the southern walls with two small oblong towers (Ippokratous Street) still exists today. On the contrary, only a fragment of the northern walls situated opposite the entrance of the Nerantzia Castle and supporting the mound of the Plane tree of Hippocrates still exists today. At the eastern bastion you can see the coats of arms of Juan Fernandez de Heredia and his chargé d’affaires in Kos, commander Schlegelholz above the gate. The oblong battlements and the arrow slits further up on the same wall were added during the Ottoman Greece period. The house of Francesco Sans on Akti Miaouli Street, who was the Knight Hospitaller commander of the island, still exists today. The house is attached to the perimeter wall and was built in 1514. It has two vaulted spaces with carved moldings that used to be a coffee house during the Ottoman Greece period. Opposite the museum in the west you will notice the Tax Gate. Its lintel is made of carved stone with a discharging arch over it, above which a projecting defense gallery with machicolations still exists today.
The medieval churches of Panagia Gorgoepikoos, Agios Ioannis Prodromos, the New Martyr Ioannis Nafkliros, Agios Konstantinos and Panagia Katevati have all been preserved inside the old town. The Muslim temple of Lotzia at the Plane tree of Hippocrates Square, that was built in 1786 by the Algerian admiral Djeza’irli Hasan Pasha, the Defterdar mosque, that was built by Ibrahim Effendi, the finance minister of the Sultan at Eleftherias Square and the Hatzi Pasha mausoleum at the corner of Ippokratous and Mitropoleos Street, are all monuments of the Ottoman Greece period that have been preserved to this day.