Legend says it was built by the ancient gods; the ring fort was known as the Sun Palace and was held sacred. Traces of ancient earthworks, dating to the early Iron Age, surround the fort, enclosing an area of about 5 acres (0.02 km2). The fort itself was probably built in the early centuries of the Christian era. From the 5th to the 12th century AD it served as the royal seat of the O Neill sept of Aileach; it was destroyed by Murtogh O Brien, king of Munster in 1101. To make the demolition complete, the king ordered each of his soldiers to take away a stone from the fort. Grianan of Aileach was reconstructed by Dr Bernard of Derry in 1870, but archaeologists are doubtful about the inner restoration. Surrounding the stone fort are three concentric low walls which formed part of the original fortification of the fort.