A rich mix of architectural styles reflects the castle's complex history and role as both stronghold and seat of Kings. The tiny St Margaret's Chapel, Edinburgh's oldest building, dates from the 1100s; Crown Spuare, the principal courtyard, was developed in the 15th century; the Great hall with its impressive hammerbeam roof was built by James IV, the Half Moon Battery was created in the late 16th century; and the Scottish National War Memorial was added after the First prisoners of war were held in the 18th and 19th centuries; The 'Honours of the Kingdom' exhibition telling the story of Scotland's Crown Jewels - saved from Cromwell to become some of the oldest surviving regalia in Europe; the Stone of Destiny - taken to Westminster Abbey in 1296 and returned to Scotland 700 years later; the One O' Clock Gun and a display on the history of time guns and timekeeping; and the giant medieval siege cannon Mons Meg, once again standing proudly on the castle ramparts.