This book covers the armies of the Roman Empire and its opponents from 25 BC to 493 AD: From the first Emperor, Augustus, until the final demise of the Western Roman Empire.
Most of the eventual territories of the Roman Empire had already been conquered by 25 BC – see our companion volume, “Rise of Rome”. However, after a period of consolidation and re-organisation under Augustus, some further territorial expansions were made. Britain was invaded in 43 AD and successfully conquered. The Rhine/Danube salient was conquered in Germany in order to shorten the frontier. Dacia, north of the Danube, was conquered by 106. The former client states in the East were progressively annexed and made into Roman provinces, advancing the Empire to the Parthian frontier.
The resulting borders were maintained until the 3rd century, when a series of wars against Germanic tribes, and endemic civil wars, resulted in the loss of the Rhine-Danube salient and Dacia, leaving the Northern frontier of the empire firmly on the lines of the Rhine and Danube.
By the end of the 3rd century, the constant pressure on all of the borders of the empire made necessary a reorganisation. Under Diocletian the army was expanded and the empire was divided into Eastern and Western halves, each under its own Augustus (senior emperor) and Caesar (junior emperor). Less emphasis was placed on forward defence, and more on defence in depth, with gradually expanding central field armies. As time went on the Eastern and Western parts of the Empire became more separate and cooperated less.
Many underlying reasons have been proposed for the eventual fall of the Western Roman Empire, but from a military point of view the main feature was increasing pressure on the northern frontier from waves of displaced Germanic tribes, pushed westwards by the advance of the Huns. In the early 5th century the frontier defences collapsed. Migrating tribes pushed their way into the Empire and seized areas of territory. Initially a favourable “spin” was put on this and these tribes were officially granted land and employed as foederati to help defend against the further waves of tribes coming up behind. As the century progressed, however, several tribes dispensed with this polite fiction and set up their own independent kingdoms in former Roman territories. The last puppet emperor in Italy, Romulus Augustulus, was deposed by the foederate Odoacer in 476. By 493, Italy was ruled by the Ostrogoths, southern Gaul (southern France) and most of Spain by the Visigoths, northern Gaul (northern France) by the Franks and North Africa by the Vandals.
The Eastern Roman Empire, with its capital at Constantinople (modern Istanbul), by contrast, weathered the storms of the 5th century, and even re-conquered several portions of the Western Empire in the 6th century. Known to historians as the Byzantine Empire (but to its inhabitants as the Roman Empire) it continued until Constantinople fell to the Ottoman Turks in 1453. (See our companion volumes, “Byzantium and Islam”, “Swords and Scimitars” and “Rise of the Ottomans”.)
Kushan or Indo-Skythian
Dacian or Carpi
Early Visigothic or Early Vandal
Early Frankish, Alamanni, Burgundi, Limigantes, Quadi, Rugii, Suebi or Turcilingi
Early Anglo-Saxon, Bavarian, Frisian, Old Saxon or Thuringian
Early Ostrogothic, Herul, Sciri or Taifali
Gepid or Early Lombard