Island Castle was built in several phases. During the first phase, in the second
half of the 14th century, the castle was constructed on the largest of three
islands of lake Galvė by the order of Grand Duke Kęstutis. The second phase of
construction continued until 1409. This phase is regarded as the major
development in the history of the castle. During the second phase, two wings
were added in main castle, and on the southern side a 35 m high strong central
tower was built. This tower had movable gates which separated the main castle
from the forecastle. The expansion of the forecastle in the early 15th century
marked the third phase of Trakai's development. The walls of the forecastle were
strengthened to a thickness of 2.5 meters and raised with additional firing
galleries. Three major defensive towers were constructed on the corners.
Trakai Island Castle lost its military importance soon after the Battle of Grunwald, when the chief enemy of the Grand Duchy of Lithuania was defeated by the Lithuanian-Polish army. The castle was transformed into a residence and newly decorated from the inside.
During the wars with Muscovy in the 17th century, the castle was damaged and was not reconstructed again. It gradually fell into disrepair. After World War II, a major reconstruction project was begun in 1946; active work started in 1951-1952. The major portion of the reconstruction was finished in 1961. The castle was reconstructed in a 15th century style.