Hillforts largely declined in importance in the second half of the second century BCE, with many being abandoned. Probably around this period, the first recorded invasion of Britain took place, as southern Britain was largely conquered by warrior-elites from Belgic tribes of northeastern Gaul – whether these two events are linked to the decline of hillforts is unknown. By the Roman conquest, the "oppidum" at Venta Belgarum, modern-day Winchester, was the "de facto" regional administrative centre; Winchester was, however, of secondary importance to the Roman-style town of Calleva Atrebatum, modern Silchester, built further north by a dominant Belgic polity known as the Atrebates in the 50s BCE. Julius Caesar invaded southeastern England briefly in 55 and again in 54 BCE, but he never reached Hampshire. Notable sites from this period include Hengistbury Head (now in Dorset), which was a major port.