Segontium is a Roman fort for a Roman auxiliary force, located on the outskirts of Caernarfon in Gwynedd, north Wales. It probably takes its name from the nearby River Seiont, and may be related to the Segontiaci, a British tribe mentioned by Julius Caesar. The fort was founded by Agricola in 77 or 78 AD after he had conquered the Ordovices. It was the main Roman fort in the north of Roman Wales and was designed to hold about a thousand auxiliary infantry. It was connected by a Roman road to the Roman legionary base at Chester, Deva Victrix. Unlike the more recent Caernarfon Castle alongside the Seiont estuary, Segontium is located on higher ground giving a good view of the Menai Straits.