The Roman Frontier with Germania 70 CE

The Rhine and Upper Danube were the natural frontiers that secured the borders of Rome’s dominion. These natural barriers were transformed into a fortified border that marked the edge of Empire and hence the civilized world. These rivers protected the Roman world with the exception of a gap stretching from Mogontiacium (Mainz) to Regina Castra, a 300-km wide corridor that permitted the mass incursions of people into the Empire by land. It was hence this section, the most vulnerable, which became the most heavily fortified. The first Emperor who began to construct fortifications was Augustus, shortly after the Battle of the Teutoburg Forest in 9 CE, when an alliance of Germanic tribes ambushed and destroyed three legions. The German frontier was gradually consolidated from the death of Augustus in 14 CE. In 69 CE the Batavian revolt, which took place against the chaotic backdrop of the ‘year of four Emperors’, resulted in the destruction of two legions in the Rhine delta. Attempts to quell the mutiny were hampered by poor communications between the Rhine and Danube forces, reinforcing the need for a permanent military presence along the frontier. The fortifications, or limes, that were constructed along this border between c 70 CE and 260 CE were marked by a stout timber palisade, or in some areas a stone wall, with forts, fortlets and watchtowers set back from it, creating a broad boundary. They were manned by a remarkably small number of troops and probably served as an early warning system if mass incursions were attempted; movements of small groups across a porous border could also be monitored and controlled.