In 58 BCE, events in Gaul demanded Roman intervention. A king of the Germanic Suevi, Ariovisitus, attacked the Aedui, a Roman ally, while the Helvetii were threatening to encroach from Switzerland into Gallia Transalpina. The Roman governor there, Julius Caesar, scenting glory, reacted swiftly, crushing first the Helvetii, then Ariovisitus. The following year, Caesar’s campaign against the Belgae and Nervi narrowly averted disaster before his ultimate victory conferred control over modern Belgium. From this northern bridgehead, Caesar moved down the Atlantic coast, defeating the Veneti of Brittany in an amphibious campaign. Now possessed of a navy – and clearly acting beyond his remit – Caesar launched an opportunistic invasion of Britain, defeating Cassivelaunus (54 BCE). A chain-reaction of rebellions swept Gaul, incurring Caesar’s retribution and the near extermination of the Eburones. This was to prove the prelude to the gravest rebellion, led by Vercingetorix, finally trapped and defeated by Caesar at Alesia (52 BCE); within two years the conquest was complete.