The main medieval monument of Kos is the castle, located at the entrance of the port, with a rectangular plan and a typical example of imposing defensive architecture of its time.
It was built by the Knights of the Order of St. John of Jerusalem, who occupied the island in 1314, on an islet on the south side of the port of Kos and communicated by a drawbridge with its walled city, "Chora", which occupied the current archaeological site of the ancient Agora and Port. As is known, the Knights of the Order of St. John of Jerusalem, after being expelled from the Holy Land, they ended up in Rhodes and organized a defense system in the area with the aim of the safe movement of pilgrims and travelers to the Holy Land. The danger of Ottoman invasions and pirate raids make the castle of Nerantzia one of the most important strongholds of Western civilization. The first written evidence of the existence of the castle is made in 1431, in a reference to the mission of a garrison but its older architectural form does not date back before the middle of the 15th century.
The construction and repair of the fortifications in Nerandzia during the period of the Knighthood (1337-1522) can be distinguished in two phases, which are due to the transition from the use of traditional weapons to the use of gunpowder weapons after the middle of the 15th century. Thus, in the first building phase, the rectangular inner enclosure with straight walls and corner circular towers is placed, while after the middle of the 15th c. the fortification is strengthened with the construction of the outer enclosure, with ramparted walls and impressive bastions. After 1522 and the occupation of Rhodes by the Ottomans, Nerandzia was handed over to the sovereignty of the Sultan until 1912, when the island was occupied by the Italians.
The castle of Nerantzia presents two main chronological phases that belong to the period of the Knighthood and extensive repairs and additional works in the period of the Ottoman rule. The inner precinct belongs to the oldest phase of the Knighthood, which dates according to the built-in coats of arms of the Grand Masters and the prefects of Kos to the third quarter of the 15th century. It is separated from the outside on the south, west and north sides by an inner moat. The entrance to the inner enclosure opens into a square tower on the SW side of the castle and is constructed of marble pilasters and a marble lintel bearing the coat of arms of the Grand Master commander of the Order of the Knights of St. John d'Aubusson, as well as the commander of Co Carmadino. with the date 1478.
The corridor of the gate is sheltered by ten monolithic granite columns, which come from the early Christian basilica of Limanos. The metapyrgias consist of vertical isostructural masonry, crowned with a perimeter and strong ramparts. In their construction, abundant building material is used from ancient buildings as well as marble inscriptions. Of the four corner towers of the inner precinct, three are preserved: The outer precinct is an excellent example of the experience that the Ioannites had acquired in the execution of fortification works after the siege of Rhodes by the Turks in 1480. It is rectangular with four bastions at its corners, solid constructions with an outer slope that is strongly inclined to repel cannon fire. It communicates with the inner enclosure by an inclined arched bridge. In the same period, the outer moat on the south side was also formed. It communicated with the walled medieval city, "Chora", with a drawbridge and had an original width of 33m. During the period of the Italian occupation, it was formed into a wide avenue, today's street of Phoinikas.
The bastions of the outer enclosure have vaulted corridors inside that lead to side rooms with cannon ports. To deal with the concentration of smoke above the cannon nests, air ducts were constructed. The roof of the bastions is formed with a strong parapet and cannon ports. The polygonal bastion of D'Aubusson (1476-1503) is probably the first to be built. Work began in 1489 with the aim of protecting the northern side of the castle. In the SW corner, the bastion of the Grand Master Fabrizio del Carreto (1513-1521) dominates the harbor of Kos, with a circular plan and with only openings the cannon ports.
On the east side of the outer enclosure is D'Aubusson's square bastion (1476-1503) with a square ground floor perimeter corridor with nine cannon ports and vents for ventilation and a stone staircase leading to a first level and roof. The post-bastion spaces are built with careful stonework and most of them have escarpments. They end in a parapet with ramparts and a perimeter wide enough for the men to move around.
Editor: Fotini Anastasopoulou