Stirling Castle - crag and tail
Like Edinburgh Castle, Stirling Castle stands on a plug of hard volcanic rock. They are both examples of what geographers call 'crag and tail'. During the Ice Age, glacial ice flowing east from the Highlands, eroded away most of the rock it came up against, until it came up against these hard igneous rocks. The ice parted and flowed around the volcanic plugs, leaving a 'tail' of the softer surrounding rock on the downstream side in the process.
Both Edinburgh and Stirling Castles are unapproachable from the sides last scoured by glacial ice 20,000 years ago, and have to be approached along the tail from the east. Although forming a convenient approach for those welcome to the castle, the tails also provided an easy approach for besieging armies, which is why in both cases, a large clear area occupies the ridge-top immediately below the castle. The areas where the tattoo is now held below Edinburgh Castle, and where cars and coaches park below Stirling Castle, were kept clear to provide uninhibited fields of fire for the guns on the castles walls, and limit the cover from fire available to the bad guys!