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 Polish-Lithuanian army. The castle was transformed into a residence and newly decorated from the inside. New frescos were painted on its walls, which have been partially preserved. Foreign emissaries were welcomed in the Ducal Palace. It is known that Jogaila visited the castle thirteen times between 1413 and 1430. In 1414, the Flemish traveler Guillebert de Lannoy described the castle in these words:
