ENDuring the establishment of the Lithuanian state, Trakai was one of the main political and military centres. The three castles (Old Trakai and Peninsula and Insular castles of New Trakai) residences of the grand dukes of Lithuania and their sons have been and are frequently visited. Indeed, the Insular Castle built in the second half of the 14th-the beginning of the 15th centuries was most' modern in Lithuania. Analysis of the masonry of the castle revealed that it was built in a few stages. A three-block palace of Romantic style with a front castle was the first to appear in the largest northern isle. The unfinished castle was set on fire. The second Gothic stage of building began in the 15th century. Having gained power in the GDL, Vytautas resumed his father’s undertaking and finished the Insular Castle extending and modernizing it according to a new plan. It is supposed that an Order architect supervised the works. Stone was the main building material. Aleksandras Jogailaitis was the last duke who resided in Trakai. The fact that the national treasury and the Lithuanian Metrica were stored at the Trakai castle shows its exclusive role. Not only money but also treasures, decorations, regalia of the Grand Dukes, weapons, and gunpowder were stored at the treasury.The castle was partly ruined in the summer of 1655 during the unsuccessful war with Russia and Sweden. The city, both castles and the church were burned down. A museum has been established in the restored and investigated Trakai Insular Castle. The museum has a standing and a movable expositions. It is also a place of cultural events. The castle is visited by official delegations as in the Middle Ages. It has been visited by the Danish Queen Margaret II, Swedish King Carl Gustav XVI with his wife Sylvia, presidents of Bulgaria, Poland, China, Macedonia, Portugal, Romania, Slovenia, Turkey, Latvia, Uzbekistan, and Estonia, prime ministers, ministers and ambassadors of many countries.