Out here on the eastern edge of Württemberg, where the Jagst valley widens into rolling farmland below the Ellwangen hills, the Romans drew a line across the map and then built it in stone. The fort at Rainau-Buch, which the ride labels Reinau-B, sat just behind the Raetian Limes, the frontier that ran from the Rhine toward the Danube. What you find today is a grassy rectangle with low reconstructed wall footings, the outline of a bath house, and the traces of the civilian village that grew up outside the gate, where traders, families and off-duty soldiers lived the way garrison towns always do.
The ground explains why the frontier ran here. It is open, gently rising country with long sight lines, good for watching and signalling. A few kilometres away the Limes Gate at Dalkingen, a showpiece gateway the Romans built across the frontier wall, now sits under a modern glass shelter, and it is worth the short detour if the protective building is open. The Bucher Stausee, a small reservoir right beside the fort site, gives the place a lakeside feel in summer, with walkers, a few anglers and swallows working the water at dusk.
The riding around here is relaxed rather than dramatic. Country roads loop between Rainau, Westhausen and Hüttlingen through wheat, maize and patches of spruce, with gentle climbs, plenty of open bends and village speed limits that come up quickly, so keep an eye out for the yellow signs. The A7 motorway runs close by, which makes the place easy to reach and easy to leave, but the better way in is via the minor roads from the Jagst side. Spring and early autumn are the sweet spots; on hot summer afternoons the farm traffic and the tractors are out in force.
For practical things, Westhausen and Hüttlingen are both towns of several thousand people with fuel and a bakery or two, and Ellwangen, about six kilometres away, is the real centre: a handsome small town with a castle on the hill, the pilgrimage church of Schönenberg looking down on it, cafés around the old market and every service you need. It is a good place to take a long lunch before heading west along the frontier toward the Swabian Forest. The fort itself has no facilities beyond paths and information boards, so bring water if you plan to walk the circuit of the Limes park.