South of Gunzenhausen the old frontier of the Roman Empire ran across the countryside in a ruler-straight line, and the numbered watchtowers are the markers for that line. This is the Raetian Limes, the stretch that, from the second century onward, was built from timber and then stone to protect the province of Raetia from the Germanic tribes to the north. The numbers 13/41 to 13/45 simply describe a cluster of tower sites on the surveyor's map. Most of them have been reduced by farming and time to low mounds and gentle banks in the fields, so what you actually find is landscape rather than masonry.
That landscape is the pleasant part. The ground here is the southern end of the Franconian Lake District, with fields of rape and barley, small woods, drainage ditches and the shining surfaces of the Altmühlsee and the Kleiner Brombachsee close by. The Altmühlsee is an artificial lake created in the 1980s to manage water, and today it is a reserve of great importance for migrating birds, which makes the area fine for a slow morning with binoculars. Muhr am See is a small lakeside village with a neat shoreline and a number of campsites.
For the motorcyclist, roads here are an easy rhythm of long straights and mild bends, with farm traffic, cyclists and families on holiday in July and August. The surface is generally good, and views open across the lakes and farmland. Few spots demand much concentration, so this is a day for letting the mind wander towards the Romans, who simply marched across this country and drew a line on it, which the men posted in a draughty tower would have found far less relaxing than we do now.
Gunzenhausen, six kilometres away, is the logical stop. It has fuel, supermarkets, bakeries and ice cream, a historic town centre with half-timbered houses and a good riverside promenade along the Altmühl. A little further south, Weißenburg has Roman baths and a museum that give the line some real substance. Spring and early autumn are the best seasons, with the lakes quiet and the fields in good colour.