Antimachia Castle, Medieval fortress in Antimachia, Greece.

Antimachia Castle is a medieval fortress on a plateau about 170 m above Kardamena Bay, 3 km east of Andimachia on Kos. Its 970 m wall follows the hill as an irregular pentagon, with no towers rising above the wall walk. The northwest main gate was later protected by a horseshoe-shaped bastion; above the inner gate sits the coat of arms of Grand Master Pierre d'Aubusson with the year 1494.

The Knights of Saint John built the fortress between 1322 and 1346 on the site of a Byzantine castle; Grand Master Helion de Villeneuve is named as its builder. In June 1457 an Ottoman force besieged it for 23 days, and 15 knights with about 300 islanders held out, losing 15 defenders while the besiegers suffered 1,000 dead and over 2,000 wounded. Kos passed to Ottoman rule in 1522, and a small garrison stayed until 1871.

Inside the walls stand the single-nave chapel of Agios Nikolaos, with 15th- and 16th-century frescoes partly preserved in its eastern apse, and the church of Agia Paraskevi, built in 1705. A stone slab above the chapel entrance carries three coats of arms, including that of Grand Master Fabrizio del Carretto, and the date 1520. A mosque also existed here during the Ottoman period; only ruins remain of the Panagia Eleimonitrias church.

This fortress sits on its own hilltop removed from the main village, requiring a separate journey to reach it. Expect uneven ground, open ruins with limited shade, and exposed stonework that demands sturdy footwear.

Records from medieval times show this fortress once served as a place where convicted knights faced imprisonment. This darker function reveals a side of the knightly order often overlooked by visitors.