Watch Bloody Foreigners online: Episode 4 The Untold Invasion of Britain

In a mountainous land, at the limit of its influence, the world's only superpower gets bogged down in an asymmetric war against a deadly insurgency. It sounds like a familiar story, but this is history from almost 2,000 years ago. Brought to life with animated sequences based on contemporary Roman sources, this is the extraordinary story of a very bloody foreigner: the little-known Roman Emperor Septimius Severus, an African who seized Rome's Imperial throne in a vicious civil war and then fought a brutal campaign in Britain, transforming the country in his wake. In 207AD, Britain was just a far outpost of the mighty Roman Empire with the north holding out. With a vast army, Severus marched over Hadrian's Wall. Using guerrilla tactics, the Britons attacked isolated Roman patrols, and then melted into the mountains. Severus wasted four years and thousands of Roman lives in a futile attempt to defeat his invisible enemy until his demise in York in 211AD. His campaign only served to create a new enemy north of The Wall and helped forge the English/ Scottish divide that is familiar to us today. This programme follows Severus's trail from the magnificent remains at Lepcis Magna in the Libyan Desert, to the military hardware left by his campaign in Britain.

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