History Pre-history of the Castle Rock Geology The castle stands upon the plug of an extinct volcano, which is estimated to have risen about 350 million years ago during the lower Carboniferous period. The Castle Rock is the remains of a volcanic pipe, which cut through the surrounding sedimentary rock before cooling to form very hard dolerite, a type of basalt. Subsequent glacial erosion was resisted by the dolerite, which protected the softer rock to the east, leaving a crag and tail formation. The summit of the Castle Rock is above sea level, with rocky cliffs to the south, west, and north, rising to a height of above the surrounding landscape. This means that the only readily accessible route to the castle lies to the east, where the ridge slopes more gently. The defensive advantage of such a site is self-evident, but the geology of the rock also presents difficulties, since basalt is extremely impermeable. Providing water to the Upper Ward of the castle was problematic, and despite the sinking of a deep well, the water supply often ran out during drought or siege, including during the Lang Siege in 1573. Earliest habitation Archaeological investigation has yet to establish when the Castle Rock was first used as a place of human habitation. There is no record of any Roman interest in the location during General Agricola's invasion of northern Britain near the end of the 1st century AD. Ptolemy's map of the 2nd century AD shows a settlement in the territory of the Votadini named "Alauna", meaning "rock place", making this possibly the earliest known name for the Castle Rock. This could, however, refer to another of the tribe's hill forts in the area. The Orygynale Cronykil of Andrew of Wyntoun (c. 1350 – c. 1423), an early source for Scottish history, names "Ebrawce" (Ebraucus), a legendary King of the Britons, as having "byggyd [built] Edynburgh". According to the earlier chronicler, Geoffrey of Monmouth (c. 1100 – c. 1155), Ebraucus had fifty children by his twenty wives, and was the founder of "Kaerebrauc" (York), "Alclud" (Dumbarton) and the "Maidens' Castle". The 16th-century English writer John Stow (c. 1525 – 1605), credited Ebraucus with building "the Castell of Maidens called Edenbrough" in 989 BC. The name "Maidens' Castle" ( or ) occurs frequently up until the 16th century. It appears in charters of David I (r. 1124–1153) and his successors in