Built in the 15th century by one of Scotland's most powerful families, the Crichtons, Blackness was never destined as a peaceful lordly residence, its enduring roles were those of garrison fortress and state prison. In the 16th century, the castle's defences were strengthened to make it one of the country's most formidable artillery fortifications. Besieged and damaged in 1650 by Cromwell's army, it was used, after its restoration, to incarcerate Covenanters. After the 1707 Treaty of Union, Blackness ceased to be a state prison and became a minor garrison. During the wars with France between 1759 and 1815 it held prisoners of war, then in 1870 was converted to an ammunition depot. Finally in the 1920s, the castle was conserved as an ancient monument. The vexed spirit of an Angry Knight is said to have chased a female witness out of the castle during a sightseeing tour. Banging sounds have also been reported, with no source ever being found.