Behind the name is a number system, because the Limes archaeologists gave every watchtower a code. WP means Wachposten, a watchtower, and 4/72 means the seventy-second one on the fourth section of the frontier, the one that crosses the Wetterau. This pair of towers stands in farmland near Hungen, in central Hesse, and the Romans placed them on a gentle rise from which a watchman could see across the open plain and signal to the next tower along the line.
The Wetterau is a broad, fertile basin north of Frankfurt, with rich loess soil that has been farmed since the Neolithic. The Romans wanted it. They pushed the frontier out so that it looped around the basin in a great arc, instead of following the Taunus ridge, and farms and estates called villae rusticae fed the garrisons. The border here was marked by a palisade and, later, a ditch and rampart, with small stone watchtowers every few hundred metres. Today the line shows up mostly as a low bank, a row of trees or a faint ditch in the field.
Hungen is a small town of about 4,600 people, with a castle and a half-timbered centre, and Lich, about 8 km away with 13,500 people, is the better place for fuel and supplies, and also known for its brewery and for the Solms family's castle. The surrounding roads are quiet farm lanes between fields of wheat, sugar beet and rapeseed, with the Vogelsberg, an extinct volcano, rising to the east. This is easy, relaxed riding, pleasant in late spring and early autumn, though traffic on the main roads can be busy with commuters heading towards Giessen and Frankfurt.
The Upper German-Raetian Limes is a UNESCO site, but much of it is subtle on the ground, so it helps to read the information boards. In summer the wide fields give a long view, and in autumn mist lies in the hollows in the morning. There is a good chance of seeing red kites circling overhead, a bird that is common in this part of Germany. A coffee and a piece of Streuselkuchen at a bakery in Hungen make a comfortable break, and the church towers of the villages on the plain give you a sense of how the landscape is dotted with life.