Between Rengsdorf and Anhausen the Westerwald is open farmland and beech woods, and a Roman frontier ran straight through it. The Upper German-Raetian Limes, listed by UNESCO in 2005, started on the Rhine near Rheinbrohl and ran for hundreds of kilometres to the Danube, a line of timber towers, a palisade, and in places a ditch and bank. The code WP 1/39 a is not poetry, it is bookkeeping: the old German Reichs-Limeskommission numbered the frontier by section and then by watchtower, and archaeologists still use their numbers. Here, a section of the line survives as a low bank and shallow hollow in the grass, which you will walk past without noticing unless someone points it out.
That is the honest summary of most Limes stops. There is not a wall to climb, only a faint ridge and an information board, and the pleasure is in picturing a legionary or auxiliary soldier on a cold morning watching smoke rise from the next tower. The Romans chose their line carefully, along ridges and with views, so the ride here is a ridge ride in the soft sense, with long gentle gradients and farm lanes joining the main road. Surfaces are generally good but narrow, with tractors, cyclists and the occasional horse.
The towns nearby are all small, with Anhausen, Melsbach and Rengsdorf each a couple of thousand people or fewer, so for serious fuel and a proper lunch the answer is Neuwied, a short run down to the Rhine. Neuwied itself is a planned town, laid out by a count in the seventeenth century with a policy of religious tolerance that drew Moravian Brethren, Mennonites and others, and its streets are unusually regular for the region. The Rhine is the better backdrop for an afternoon, with ferries, barges and a gravel bank for sitting.
Plan this stop as a pause between bends rather than a destination. A local bakery coffee, a look at the board, a minute with the grass. The Westerwald weather changes fast, so check the sky, and note that autumn mist in the valleys makes the ridge top feel like an island. Spring, when the beech is bright and the farmers are out, is the nicest time.