borders of the Roman Empire

The borders of the Roman Empire, which fluctuated throughout the empire's history, were realised as a combination of military roads and linked forts, natural frontiers (most notably the Rhine and Danube rivers) and man-made fortifications which separated the lands of the empire from the countries beyond.

The word limes is sometimes used by modern scholars to denote the frontier of the Roman Empire but was not used by the Romans as such. After the third century it was an administrative term, indicating a military district, commanded by a dux limitis. The Latin noun limes had a number of different meanings: a path or balk marking off the boundaries of fields; a boundary line or marker; any road or path; any channel, such as a stream channel; or any distinction or difference between two things. In Britannia the Empire built two walls one behind the other; for Mauretania there was a single wall with forts on both sides of it. In other places, such as Syria and Arabia Petraea, there was no continuous wall; instead there was a net of border settlements and forts occupied by the Roman army. In Dacia, the limes between the Black Sea and the Danube were a mix of the latter and the wall defenses: the Limes Moesiae was the conjunction of two, and sometimes three, lines of vallum, with a Great Camp and many minor camps spread through the fortifications.