The correct answer is C. The Roman pull-out from Britain.
Indeed, the soldier Roman soldier Flavius Claudius Constantinus decided to take the title of Western Roman Emperor in 407 A.D. (5th century), adopting the imperial name of Constantine III. He failed, however, to protect Roman Britain from Anglo-Saxon invasions and raids and his rule was ultimately rejected by the Roman-Britons who decided to arm themselves. and organize their own protection. They also failed to protect their territory from these invasions and were conquered by the Anglo-Saxons, who ended up dividing the territory into seven Saxon Kingdoms, the Heptarchy.
It was during this struggle that he received a blow on the head which seems to have tipped the whole thing over into violence and the four knights fell on him with their swords. He died later that afternoon on 29 December 1170.