Late Roman Republic, Gaius Julius Caesar (=Caesar; fl.85-44 BC): Caesar’s Reduction of Gaul (58-56 BC), Introduction

Gaul included France, Belgium and Luxembourg; parts of the Netherlands, Germany and Switzerland west of the Rhine; and parts of Northern Italy. Gallia Comata (‘long-haired Gaul’), also called Tres Galliae (‘Three Gauls’), comprised: Gallia Celtica (Celts), the largest, in the northwest, west, centre and east; ~Belgica (Celts and Germans) in the northeast; and ~Aquitania (Celts and Aquitanians) in the southwest. 

The Romans conquered Cisalpina in 191 BC and Narbonensis (south and southeast) in 121 BC. In 113 BC the Cimbri and the Teutones invaded Gaul, and were almost annihilated by the Romans in 102 BC (Teutones) and 101 BC (Cimbri).

Gallia Celtica became an attractive target for migrating warrior populations from Germany and Switzerland. In the 70s BC the Celtic Sequani tribe (east), who were fighting for their survival against the Celtic Aedui tribe (central-east), made an alliance with Ariovistus (fl.71-58 BC), king of the German Suebi tribe east of the Rhine. In 71 BC he crossed the river with fifteen thousand warriors drawn from a confederation of German tribes and defeated the Aedui. 

After a battle in 61 BC at Magetobriga where he defeated a combined Celtic army, he requested recognition from Rome as a rightful king and was declared a ‘friend of Rome’. It was thought that he would be a useful counterbalance to the dangerous Celtic tribes, but then he began show further ambitions in the west: he settled west of the Rhine and by 58 BC he was ruling over more than one hundred and twenty thousand Germans and had taken over two thirds of Sequani territory.

When Caesar arrived in Northern Italy the forces available to him consisted of four legions (VII to X), three of which were based in Aquileia on the eastern border of Cisalpina to guard against attacks from the Illyrians and the fourth in Narbonensis, perhaps at the capital Narbo.