The Kos Town Castle (Neratzia) is situated at the entrance of the Kos Harbor. It faces the Halikarnassos Castle (Saint Peter Fortress) situated just opposite on the Turkish coasts with which it collaborated to control the strategic straits between Kos and Turkey. The Kos Town Castle was initially built on an islet that blocked the entrance of the ancient harbour and its entrance is situated at the Square of the Hippocrates Plane Tree, where a bridge crosses the Palm Tree Avenue which used to be a moat until the beginning of the 20th century. At the end of the 14th and the start of the 15th century, the island was densely planted with lemon and bitter or sour oranges and the island with its fortress were then renamed Nerantzia (sour orange tree in Greek).
The Neratzia Castle, in its present form, was built by the Knights of St-John of Jerusalem who ruled the island from 1314 to 1522. When H. Schlegelholtz was Commander of the island (1386-1412), the Knights of St. John undertook major military works that fortified the perimetrical city wall, the fortress and the great strongholds or ramparts, enlarging and strengthening the fort on every side. The perimetrical wall of the city was built from 1391 to 1396 with every kind of ancient material found in the area. The construction of the Saint Peter Fortress in Halicarnassos is also attributed to Schlegelholtz.
Fortification works of the outer fortress of Nerantzia were undertaken from 1498 onwards, due to the intensification of Turkish offensive activities. Between 1505 and 1508, the western side of the castle facing the harbour was constructed, whereas the bridge which connects the outer fortress with Hippocrates’ Plane Tree Square must have been constructed between 1500 and 1510.
Inner and outer Keep of the Neratzia Castle
The inner Keep of the Kos Town Castle (Neratzia) was built around the 14th century while the outer Keep dates from the end of the 15th/beginning of the 16th century. Between the two keeps there is a moat and the entrance to the Inner Keep is a sloping bridge.