Around Haltwhistle the wall climbs on to the Whin Sill, a hard ridge of dark volcanic rock that runs across northern England like a spine, and the effect is among the most dramatic on the whole frontier. The wall rides the crest of crags, rising and falling over the rock, with a steep drop to the north and long views over moorland, and the Roman engineers made full use of the natural defence. The vallum, a broad flat-bottomed ditch with mounds on either side, runs in the valley to the south, and it marks the boundary of the military zone behind the wall.
The road in the title is the Military Road, the B6318, which runs close to the line of the wall for many miles. It was built after the Jacobite rising of 1745, when General Wade found that he could not move his army across the north of England quickly enough, and the road builders used wall stones as foundations, which tells you how the wall suffered. Today the Military Road is a fine, undulating ride with long straights and sudden crests, but it is narrow in places and busy on summer weekends, so take it easy and watch for walkers crossing.
Haltwhistle bills itself as the centre of Britain, a claim based on the midpoint between the northernmost and southernmost points of the island, and it has a charming market-town feel, with a main street of stone houses. Nearby is the Roman Army Museum at Walltown, which explains the lives of the soldiers who garrisoned the wall, many of whom came from what is now Belgium, the Netherlands, Germany and Spain. Walltown Crags has a good stretch of wall, and the Cawfields area to the south has one of the best-preserved milecastles.
Weather changes quickly on the ridge, with winds, rain and mist, and the road can be icy in winter, so check conditions. Spring and autumn have the best light, and in summer the evenings are long and the heather turns purple. Haltwhistle, about three kilometres off, has a fuel station, shops, cafés and pubs, and Hexham, a larger market town further east, offers more choice. Try a pie and a pint in a local pub, or a cup of tea and a slice of cake at a village tearoom, and take a short walk along the wall before you ride on.