Upper Germanic-Rhaetian Limes

The Upper Germanic-Rhaetian Limes, or ORL, is a 550-kilometre-long section of the former external frontier of the Roman Empire between the rivers Rhine and Danube. It runs from Rheinbrohl to Eining on the Danube. The Upper Germanic-Rhaetian Limes is an archaeological site and, since 2005, a UNESCO World Heritage Site. Together with the Lower Germanic Limes it forms part of the Limes Germanicus.

The Limes used either a natural boundary such as a river or typically an earth bank and ditch with a wooden palisade and watchtowers at intervals. A system of linked forts was built behind the Limes.

Source: Wikipedia