When Rome reached the limit of its expansion several major Roman frontiers were established. These frontiers were known as Limes¹, the best known is probably Hadrian's Wall known to the Romans as the Limes Vallum Aelium, "the Aelian frontier". These had to be manned by a permanent garrison to prevent raids or invasions and provide protection of the markets and associated trade routes, and if necessary provide military support to friendly tribes.

To provide a garrison to man the defenses, the Romans created a border force known collectively as the Limitanei formed to perform this static duty freeing the legions for more important duties. Based in a static base the garrison forces enjoyed the facilities of stone built accommodation with heating, bath houses and the bars and other entertainments favoured by soldiers.

These men were properly trained auxiliary soldiers with the benefit of legionary support if required, they simply were paid less as less was expected of them, and they never fought far from home or their fortified base. The Limitanei also had the opportunity to have families in their home base.

In contradiction to common expectation once the frontier fortifications were built they were not exclusively manned by the legions. To station a legion on a fixed frontier wall, unless it was threatened with imminent attack would be a pointless waste of trained troops. The legions were only ever called for support if the wall was attacked by overwhelming numbers.

The Germanic tribes were a constant threat along the Rhine frontier and required a strong defensive barrier and a large border force and a formidable defensive system. This resulted in the construction of two a series of linked defences.

The fronteers often had some large thriving settlements built on important trade routes under the protection of the Limes, the Roman City Carnuntm in Austria ² is an excellent example, built to serve the Upper Germanic and Lower Germanic Limes

Both constructed to protect borders against incursions by armed raiders from tribes of northern Britain. In addition to the Limes Vallum Aelium in Britain the other larger defensive systems were:-

In North Africa constructed to protect borders against incursions by armed raiders from tribes of the Sahara, the legions constructed the,

The Germanic tribes were a constant threat along the Rhine frontier and required a strong defensive barrier and a large border force and a formidable defensive system. This resulted in the construction of two a series of linked defences.

This defencive system extended from the North Sea on the coast of the Netherlands over the Taunus mountains to Lorch.
Rhine at Rheinbrohl across the Taunus mountains to the river Main (East of Hanau), then along the Main to Miltenberg, and from Osterburken then south to Lorch near the towns of Schwäbisch Gmünd and Schorndorf.