The Limes was a long wall, in effect, that stretched for about 550 kilometres across Germany, from the Rhine near Koblenz to the Danube near Regensburg. It was built in stages from the first century AD, starting as a line of wooden watchtowers and a cleared strip through the forest, and then gaining a ditch, a palisade and, in places, a wall. The watchtowers were numbered by the German scholars who surveyed the line in the late nineteenth century, hence the codes such as WP 1/83, which mean watchpost number 83 in section 1. The Upper Germanic-Raetian Limes was listed by UNESCO in 2005.
Here, in the Westerwald hills north of the Lahn, the line passes through forest and farmland, and the watchtowers are small mounds or low stone foundations among the trees, with information boards, and in a few places, reconstructed towers. Nearby, the fortlet at Pfarrhofen and the other fortlets show how the frontier was held. It is a quiet and rather atmospheric place, where you can walk along the ridge and imagine a handful of soldiers watching for movements on the other side.
Bad Ems, a few kilometres away, is a nineteenth-century spa town in a narrow valley of the Lahn, where the Russian tsars, Kaiser Wilhelm I and Napoleon III took the waters. It also lent its name to the Ems Dispatch of 1870, the telegram that Bismarck edited to provoke a war with France. The elegant colonnades and the bathing halls give a different kind of history to the Roman mounds above the town.
The Westerwald is good riding country, with its forested ridges, small valleys and quiet roads, and the roads here follow the contours with tight, shaded bends and surfaces of mixed quality. The Lahn valley road is pretty, with castles above the river and the cycle path alongside. Spring and autumn are best, and in winter the hills can be icy. Traffic is light on the minor roads, but watch for farm vehicles and walkers, especially at weekends.
Bad Ems has fuel, cafes and restaurants, with all the services of a small spa town, and Koblenz is about twenty kilometres to the west. Carry a map or offline route, since signal can fade in the valleys, and use the marked Limes trail if you want to find the next tower.