An illustration of Caesar. A politician of the populares tradition, he formed an unofficial triumvirate with Marcus Licinius Crassus and Gnaeus Pompeius Magnus which dominated Roman politics for several years, opposed in the Roman Senate by optimates like Marcus Porcius Cato and Marcus Calpurnius Bibulus. His conquest of Gaul extended the Roman world to the Atlantic Ocean, and he also conducted the first Roman invasion of Britain in 55 BC. The collapse of the triumvirate, however, led to a standoff with Pompeii and the Senate. Leading his legions across the Rubicon, Caesar began a civil war in 49 BC from which he became the undisputed master of the Roman world.