Segontium Romon Fort is an impressive excavated fortification located just outside Caernarfon. It was founded by Agricola in AD77, and it was garrisoned for over three hundred years. It was the longest-held Roman fort in Wales and used to hold a 'cohors milliaria,' a regiment of about 1,000 auxiliary infantry, mainly recruited from Belgium and Germany. It was linked by Roman roads to the main legionary bases at Chester and Caerleon by a series of marching camps and other forts.