Limes Germanicus, Roman frontier fortification in southern Germany

Limes Germanicus is a line of Roman frontier fortifications running 568 km (353 mi) from the Rhine to the Danube, with an earth bank and ditch, a wooden palisade and watchtowers at intervals, and linked forts behind them. It comprised at least 60 forts and 900 watchtowers, divided into the Lower Germanic, Upper Germanic and Rhaetian Limes. Visible sections include rough light-brown and grey masonry walls with rectangular crenellations, square towers with narrow arched windows, and a watchtower with a dark grey hipped roof and a wooden balcony on a grassy mound.

Augustus began frontier fortifications after the Roman defeat at the Battle of the Teutoburg Forest in 9 AD. Domitian's advance around 83 AD pushed the frontier east of Moguntiacum, and Hadrian or Antoninus Pius later marked out the line still visible today. The frontier separated the empire from unsubdued Germanic tribes until about 260 AD, when the garrisons withdrew.

The name comes from Latin limes, a frontier path, and Germania, the Roman name for the lands east of the Rhine. Since 2005 the Upper Germanic and Rhaetian sections have been UNESCO World Heritage; the Lower Germanic Limes followed in 2021. The Saalburg near Frankfurt is a reconstructed fort with a museum of the frontier.

Many sections lie in rural areas and are accessible via regional roads or hiking trails, with some sites offering nearby parking. Information panels at several points explain the function and layout of the frontier works, making orientation easier during longer stretches.

Watchtowers along the border stood roughly one kilometer apart, allowing guards to relay messages with signal fires or smoke signals. This communication chain enabled rapid warnings throughout the entire system whenever danger approached.