WP 2/5 and 2/6 sound like spare parts, but they are the numbers archaeologists gave to two watchtower positions on the Upper Germanic-Raetian Limes, the fortified frontier Rome drew across southern Germany. Here, in the hills above the Lahn near Bad Ems, the line ran up from the Rhine and over the high ground, and every few hundred metres a tower stood with a view to the next. Today most of what survives are low mounds, traces of the bank and ditch, and in some places a reconstructed tower to give you scale. The whole frontier became part of the UNESCO Frontiers of the Roman Empire in 2005.
It helps to imagine the tower crews: a handful of auxiliary soldiers, signals by fire or horn, patrols along the palisade, and the big forts behind them for when real trouble came. The fort at Niederbieber, near Neuwied, was one of those bases. On the ground today, it is mostly forest, meadow and the sound of buzzards, which makes the scale of the old frontier all the more remarkable.
The riding is where this place earns its place on a route. The Lahn valley below is a deep, wooded cut through the slate of the Rhenish Massif, and the road along it follows every meander, with the railway and the river for company. Climb out toward Dachsenhausen or Fachbach and you get tighter, steeper bends through beech woods and onto open plateau farmland with long views. Watch for wet leaves in autumn, forestry mud on the smaller lanes and plenty of other bikers on sunny weekends, because this corner between the Rhine, Lahn and Taunus is a regional favourite. Spring and early autumn, with mist burning off the valley, are the best.
Bad Ems, five kilometres away, is the natural stop. It is an old spa town with grand nineteenth-century bathhouses along the river, and it was here in 1870 that King Wilhelm of Prussia sent the telegram Bismarck edited into the Ems Dispatch, the spark for the Franco-Prussian War. The town has fuel, cafés and bakeries, and a riverside promenade where you can sit with a coffee and watch the Lahn slide past. Koblenz and the Rhine are only a short ride further if you need a bigger town.