Limes Germanicus

The Limes Germanicus (Latin for Germanic frontier) is the name given in modern times to a line of frontier (limes) fortifications that bounded the ancient Roman provinces of Germania Inferior, Germania Superior and Raetia, dividing the Roman Empire and the unsubdued Germanic tribes from the years 83 to about 260 AD. 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.

The path of the limes changed over time following advances and retreats due to pressure from external threats. At its height, the Limes Germanicus stretched from the North Sea outlet of the Rhine to near Regensburg (Castra Regina) on the Danube. These two major rivers afforded natural protection from mass incursions into imperial territory, with the exception of a gap stretching roughly from Mogontiacum (Mainz) on the Rhine to Castra Regina.

The Limes Germanicus was divided into:

The total length was 568 km (353 mi). It included at least 60 forts and 900 watchtowers. The potentially weakest, hence most heavily guarded, part of the Limes was the aforementioned gap between the westward bend of the Rhine at modern-day Mainz and the main flow of the Danube at Regensburg. This 300-kilometre (190 mi) wide land corridor between the two great rivers permitted movement of large groups of people without the need for water transport, hence the heavy concentration of forts and towers there, arranged in depth and in multiple layers along waterways, fords, roads, and hilltops.