In the Altmühl country around Gunzenhausen the Roman frontier is a wall rather than a fence. Far to the west it was a timber palisade, earth bank and ditch, but from the edge of the Swabian Alb eastward the Romans replaced it with something sturdier, a stone wall that runs for many kilometres across Bavaria, which locals later nicknamed the Devil's Wall, the Teufelsmauer, because it seemed too big to have been made by men. The watchtowers numbered 13/51 to 13/53 belong to that stone-wall stretch, and they were small square towers of stone or timber that stood just behind the line, with a view over the valley and the next tower in the chain.
Today the traces are modest, fragments of footings, a low bank and ditch among the trees and meadows, but a few spots are marked and reconstructed. The Altmühl itself is a lazy river here, and nearby the Altmühlsee, an artificial lake created in the 1980s as part of a water transfer scheme, attracts sailors, windsurfers and birdwatchers. Gunzenhausen, a town with a Baroque church and a long history, has a museum and the Roman remains of a fort. The whole Limes is a UNESCO World Heritage Site.
Riding in the Franconian Lake District is easy and generous. The roads wander through hills and villages with half-timbered houses, small vineyards and hop fields, and the lake roads are fast and open. Surfaces are good, with the occasional long climb, and the biggest hazard is slow traffic and tractors in summer. A ride east along the Altmühl valley brings you to Treuchtlingen and Solnhofen, where the quarries produced the limestone that preserved Archaeopteryx. Autumn is beautiful, with mist in the valley, while in July and August the lake is crowded with holidaymakers.
Gunzenhausen is two kilometres away and has fuel stations, cafés and restaurants, and a pleasant old town. A local speciality is carp from the pond country around Franconia, served in autumn, and the local bakeries offer fresh pretzels and cakes. The lake has a long cycle path, and it is a nice place to pause. Remember to follow signs for forest tracks, since vehicles are banned from many, and be considerate to walkers and horse riders on the quiet lanes.