Segedunum) as well as a system of roads for the rapid transit of troops and, in some places, extensive walls. The limes consisted of fortresses for legions or vexillations (e.g. to protect the empire as a whole rather than fortifying individual settlements) are known as the limes, and continued until around 270. The coherent construction of these fortifications on a strategic scale ( i.e. He spent half of his 21 year reign touring the empire and advocating for the construction of forts, towers, and walls all across the edges of the empire. Although it was under Hadrian's rule, which began in 117, that the Roman frontier was systematically fortified. However, systematic construction of fortifications around the periphery of the empire on a strategic scale began around 40 under Emperor Caligula. Individual fortifications had been constructed by the Roman military from as early as the building of Rome's first city walls in the 6th or 7th century BC. The borders of the Roman Empire, which fluctuated throughout the empire's history, were a combination of natural frontiers (the Rhine and Danube rivers to the north and east, the Atlantic to the West, and deserts to the South) and man-made fortifications which separated the lands of the empire from the 'barbarian' lands beyond.

Vallum germanicus