The construction of both the Trakai Peninsula and Island castles started in the middle of 14th century and was concluded in the first half of the 15th century. These castles are important monuments of defensive architecture and history. The Peninsula Castle was first mentioned in written sources in the period between 1387 and 1392. Historical sources witness that there was a stone castle in Old Trakai; by the lake, in Trakai, there was a castle with two stone walls, and a timber upper castle; on the Island, stood a stone castle. At present, the Trakai Peninsula is surrounded by three lakes (Galvė, Bernardinai and Totoriškės); previously this territory was made of some separate islands or a group of islands. That way Trakai has been depicted in the old maps and plans of the town. The fortification and defence system of the town, its winter and summer road network with ramparts, wades, and bystreets, brought together separate parts of the town into single entity.
In the second half of the 14th century and in the first half of the 15th century, the stone-built Peninsula Castle stood in the junction of winter and summer roads. The castle was separated from the town by a stone wall and wide defensive moat. The building works of the stone castle took place between 1362 and 1382; the construction was continued from 1414 to 1430. This is one of the largest enclosure castles in Lithuania; it occupied the territory of 4 hectares and had 11 defensive towers of different size. The front part of the castle had a quadrangle courtyard, surrounded by a defensive wall with 6 towers. The main gate tower was build to face the town, in the middle of the defensive wall; the alternative, ‘winter’ gate was in the tower that was built in the middle of the north-eastern wall (facing Bernardinai Lake). Only the south-eastern tower had the counterforts on the corners. Presumably, the premises of the ruler of the castle were in this tower. There were no buildings in the courtyard of the castle for quite a long time; the garrison resided in the towers. After the Battle of Grunwald, the earthwork and timber fortifications around the Sacrifice Hill were replaced by masonry walls.