The Peninsula and Island Castles in Trakai, built from the mid-14th to early 15th century, are significant monuments of Lithuania’s defensive architecture and history. The Peninsula Castle is first mentioned in the “List of Russian Cities” compiled between 1387 and 1392. It states that there was a brick castle in Old Trakai, a castle near the lake in Trakai with two brick walls and a wooden upper castle, and a brick castle on an island. At that time, the current city peninsula, surrounded by three lakes (Galvė, Bernardinai, and Totoriškės), consisted of several large separate islands or island groups. Trakai is depicted this way in old city plans and maps. The individual parts of the city were unified by a system of fortifications and defenses, winter and summer roads with embankments and fords, as well as secondary streets.

At the intersection of the winter and summer roads stood the brick Peninsula Castle, built in the second half of the 14th century to the first half of the 15th century. It was separated from the city by a stone wall and a wide defensive moat. The brick construction work occurred in two main stages, the first between 1362–1382 and again from 1414–1430. It is one of the largest enclosure-type castles in Lithuania, covering an area of 4 hectares and featuring 11 defensive towers of various sizes. The front section of the castle included a rectangular courtyard surrounded by a defensive wall with six towers. The main gate tower was located in the middle of the defensive wall facing the city, while another tower in the middle of the northeastern wall (facing Lake Bernardinai) held the secondary “winter” gate. Only one tower, the southeastern one, had corner buttresses. There is the assumption that the castle’s ruler lived on the upper floors of this tower. For a long time, the castle courtyard remained undeveloped, and the garrison resided in the towers. After the Battle of Grunwald in 1410, the wooden and earthen fortifications around Aukų kalnas (Sacrifice Hill) were replaced with masonry walls. A wooden bridge connected the front section of the castle with the upper castle.