Main Limes
Germany
The Main Limes (German: Mainlimes), also called the Nasser Limes, was built around 90 AD and, as part of the Upper Germanic-Rhaetian Limes, formed the frontier of the Roman Empire in the area between the present day villages of Großkrotzenburg and Bürgstadt. In this section the limes adjoined the River Main (Moenus), which forms a natural boundary for about 50 kilometres here, so "Main" refers to the river.
Archaeological site data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).