Look south of the road near Oatens Bank, just west of Heddon on the Wall, and you will see it: a broad, flat-bottomed ditch running across the fields, with a low mound on either side. That is the vallum, and it is one of the strangest and most debated elements of Hadrian's Wall. It runs parallel to the wall, a short distance to the south, along most of its length, and it seems to have marked the rear edge of the military zone, controlling access from the south rather than defending against attack from the north. Crossings were limited to causeways opposite the forts, which suggests a kind of customs line.
Here it is unusually well preserved, partly because the farmland around has been used as pasture rather than ploughed. On a sunny morning or late in the day, low light makes the earthworks stand out, and you can follow the line by eye for some distance across the countryside. The Hadrian's Wall Path runs nearby, and walkers pass through in summer heading east toward Wallsend or west toward Bowness-on-Solway.
The road through here is the Military Road, the B6318, which was built on the line of the wall itself, and you are riding on top of Roman stones for much of the way west. It is straight, undulating and exposed, with dips that can hide oncoming traffic and crosswinds that can catch you on the high points. Watch out for farm vehicles, walkers crossing, and sheep that have found a gap in the fence.
This part of Northumberland is rural and quiet, but you are never far from services. Prudhoe and Hexham, in the Tyne valley to the south, have fuel, pubs and shops, and Corbridge, with its Roman town and pleasant streets, makes a good lunch stop. Further west, the wall becomes more dramatic around Chesters, Housesteads and Vindolanda, and the Military Road runs on toward Greenhead and Carlisle, giving one of the finest historic rides in Britain.