The Iron Age on the Isle of Man began around 500 BCE, and – as there was no Roman colonization – extended until c. 500 CE. While the Romans did not invade, the archaeological evidence suggests that marauding from Celtic neighbours was common. Man’s coastline is dotted with promontory forts, and the characteristic roundhouse locations are selected for defensibility, rather than convenience: islets (St Patrick’s Isle), marshland (Ballacagan, Ballanorris) or hilltops (the Braaid). Interestingly, although the Romans never occupied, Man may have benefited from the stationing of a Roman fleet in the Irish Sea during the Pax Romana; some readily fortified sites were abandoned during this period, and revived when Roman power waned. The typical Manx Roundhouse followed a standard Celtic design; oak posts supported a heavy, turf-insulated conical roof over a central fire. The inner circle was reserved for human habitation, with livestock housed in an outer circle reaching 98 feet (30m) in diameter.