The Romans called it the edge of the world they cared about, and in the Rems valley east of Schwäbisch Gmünd you can still trace where they drew the line. A string of watchtower sites, numbered by archaeologists along the stretch between Mögglingen, Heuchlingen and Böbingen, marks the course of the Raetian Limes, the frontier that guarded the province of Raetia in the second and third centuries. Here the frontier was a stone wall, which later locals, puzzled by the long ruined bank, called the Teufelsmauer, the Devil's Wall.
Do not expect towers standing tall. What survives is mostly a low ridge through fields and woods, occasional foundations and reconstructed outlines, and information boards along the Limes walking and cycling route. The satisfaction is in the idea: an empire stretching from Scotland to Syria, and here, in a quiet Swabian valley, men from far-off provinces stood watch over farmland that looks almost exactly the same today. The wall formed part of the Frontiers of the Roman Empire World Heritage site together with the Upper German Limes, which joins it a little to the west near Lorch.
The countryside makes for very pleasant riding. To the south rises the escarpment of the Swabian Jura, and just above Heubach the ruin of Rosenstein castle perches on a cliff with caves beneath it and a view right across the valley. The three conical hills known as the Kaiserberge, Hohenstaufen, Rechberg and Stuifen, stand to the west, and the minor roads that weave between them are full of short climbs, open bends and orchard views. The B29 along the valley floor is fast but busy, so use the side roads whenever you can. Weekends bring plenty of fellow riders and cyclists, and some Jura roads have speed limits or noise restrictions for motorbikes.
Heubach, a town of around ten thousand, is the closest place with a full range of services, and Mögglingen and Böbingen have bakeries and inns. Heubach is also, perhaps surprisingly, where the lingerie company Triumph was founded in the nineteenth century. Order Maultaschen or Linsen mit Spätzle and a local beer, and you have the whole Swabian experience in one meal.