Legions and imperial power
Roman emperors depended on the loyalty of the army. Legions defended frontiers and fought external campaigns, while military support could also decide civil wars and determine who controlled the imperial office.
Expansion and consolidation
Trajan's wars in Dacia and the East represent the high point of Roman territorial expansion. Hadrian later abandoned some eastern conquests and placed greater emphasis on defensible frontiers, permanent garrisons and inspection of provincial forces.
Frontier warfare
The Rhine, Danube, Britain, the eastern provinces and North Africa all required different military systems. Forts, roads, walls and client relationships supported Roman power alongside the field armies.
Civil wars and the later empire
Roman armies frequently fought one another during contested successions. Later Eastern Roman warfare included conflicts with Persians, Arabs, Bulgars, Turks, Normans and Crusaders, as well as repeated internal civil wars.
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