Geoffrey of Monmouth's
Historia Regum Britanniae (1136) presents a legendary Arviragus who is contemporary with the emperor
Claudius (41–54 AD). However, Geoffrey's work is highly romanticised and contains little trustworthy historical fact, rendering his account of Arvirargus suspect. According to Geoffrey, Arvirargus is a son of the former king
Kimbelinus. He succeeds to the throne of Britain after his elder brother,
Guiderius, dies fighting the invading Romans under Claudius. Arviragus puts on his brother's armour and leads the army of the Britons against the Romans. When he learns that Claudius and his commander, Hamo, have fled into the woods, Arvirargus follows him until they reach the coast. The Britons kill Hamo as he tries to flee onto a ship and the place is named
Southampton after him. Claudius is able to reassemble his troops elsewhere and he
besieges Portchester until it falls to his forces. Following Hamo's death, Arvirargus seeks refuge at
Winchester, but Claudius follows him there with his army. The Britons break the siege and attack the Romans, but Claudius halts the attack and offers a treaty. In exchange for peace and tribute with Rome, Claudius offers Arvirargus his own daughter in marriage. They accept each other's terms and Arvirargus aids Claudius in subduing
Orkney and other northern lands. In the following spring, Arvirargus weds Claudius' daughter,
Genvissa, and names the city of
Gloucester after her father. Following the wedding, Claudius leaves Britain in the control of Arvirargus. In the years following Claudius' departure, Arvirargus rebuilds the cities that have been ruined and becomes feared by his neighbours. This causes him to halt his tribute to
Rome, forcing Claudius to send
Vespasian with an army to Britain. As Vespasian prepares to land, such a large British force stands ready that he flees to another port,
Totnes, where he sets up camp. Once a base is established, he marches to
Exeter and besieges the city. Arvirargus meets him in battle there and the fight is stalemated. The following morning, Queen Genvissa mediates peace between the two foes. Vespasian returns to Rome and Arvirargus rules the country peacefully for some years. When he finally dies, he is buried in Gloucester, the city he built with Claudius. He is succeeded by his son,
Marius. Geoffrey's legendary Arvirargus appears to correspond to some degree to the historical
Caratacus, son of
Cunobelinus, who, along with his brother
Togodumnus, led the initial resistance to the
Roman invasion of 43 AD, and went on to be a thorn in Rome's side for nearly a decade after Togodumnus's death. Welsh versions of Geoffrey's
Historia call him Gweirydd and his brother Gwydr. ==Cultural legacy==