 It is also thought that South Great George's Street follows the course of an early medieval route – or possibly even the eastern boundary of a "longphort", assuming that there was a naval encampment along the eastern shore of the Black Pool at some stage in the settlement's early history.Amlaíb is known to have built a fortress at Clondalkin, eight kilometres west of Áth Cliath.This was an important seat of Norse power for more than a century.