Hunnum (also known as Onnum, and with the modern name of Halton Chesters) was a Roman fort north of the modern-day village of Halton, Northumberland in North East England. The Latinized Brittonic name “Onnum” may mean "Stream/Water", "Ash (tree)", or “Rock”; if it means "Stream", it may be a reference to the Fence Burn, where a stream touches the line of Hadrian's Wall, but if it means "Rock", it may refer to Down Hill situated to the east of it. It was the fifth fort on Hadrian's Wall, after Segedunum (Wallsend), Pons Aelius (Newcastle), Condercum and Vindobala. It is situated about seven and a half miles west of Vindobala, and is two and a half miles north of Corstopitum. The site of the fort is bisected by the B6318 Military Road, which runs along the route of the wall at that point.