Dumbarton Castle was originally a Dark-Age stronghold and the capital of the British kingdom of Strathclyde. Standing on a volcanic rock overlooking the Firth of Clyde, in the early 13th century King Alexander II founded a formidable stone castle. In 1305 during the Wars of Independence, William Wallace may have been held prisoner here and in 1333 the young King David II sheltered in the castle. In 1489 King James IV besieged Dumbarton twice and then used it as a base to destroy the Lord of the Isles. In the 16th and 17th century, the castle changed hands many times and the young Mary, Queen of Scots was kept here before going to France. Badly damaged during this period, its role as a garrison fortress continued and substantial new artillery fortifications were built in the 17th and early 18th century. Nothing survives from the Dark-Age fortress and there are only fragmentary remains of the medieval, White and Wallace Towers and the Portcullis Arch. The rest of the buildings and walls on or around the twin peaks of White Tower Crag and the Beak, date from the 18th and 19th century.