Between Hanau and the river Main, the plain is flat, fertile and dense with small towns, and it hardly looks like a frontier. Yet around the year 100 the Romans ran their Upper Germanic Limes down this way to meet the Main near Großkrotzenburg, with a palisade, ditch and a line of wooden watchtowers set at intervals of a few hundred metres. The towers on the maps are labelled by section and number, and WP 5/11 and 5/12 are two of them, neighbours in a long chain that once stretched across Germany for hundreds of kilometres.
Nothing tall stands here now. What you will find is a field edge, a row of trees, or the odd information board, but if you look at the ground you realise why the position was chosen: it is high enough to see across the open plain, with a clear sightline to the next tower. A fire or a flag could carry a warning along the line in minutes. This stretch of the frontier is included in the UNESCO listing for the Upper Germanic-Raetian Limes.
Erlensee, Rodenbach and Großkrotzenburg are all within about five kilometres, and each has fuel, a bakery and a place to eat. Hanau itself, a little farther, was the birthplace of the Brothers Grimm in the 1780s and has a monument to them in the market square. Großkrotzenburg has the remains of its Roman fort beside the Main, which is the obvious place to see the stones the towers once reported to.
Riding here is easy and unhurried. Flat, straight farm roads link the villages, with orchards, asparagus and strawberry fields in season, and a relaxed pace with a lot of cyclists. The Main bank has pleasant traffic-free stretches in the evening. There is nothing technical, but it is a satisfying link between the busy Frankfurt area and the hills of the Spessart and Vogelsberg to the east and north. Spring blossom and late summer harvest light are best, and winter fog can hang over the fields for days.