By the 6th century BC the Celts had come to dominate central Europe and regularly came into contact and sometimes conflict with the Greeks, their colonies, and the Etruscans to the south. By the 3rd century BC, Celts were often employed as mercenaries in the armies of the Carthaginian and Greek city-states. In the late 1st century BC, the Romans conquered Gaul and the Germans had settled most of central Europe. The Celtic sphere of influence receded into the British Isles where it was further diminished by the later Roman occupation of Britain..