At the time of Julius Caesar's invasion of Britain, the Trinovantes were ruled by Cassivellaunus, chief of the Catuvellauni, who had apparently deposed the father of Mandubracius at some time prior to the Roman invasion. Caesar's Gallic Wars suggests that Mandubracius sought refuge among the Romans, and that Mandubracius provided intelligence to the Roman leaders, who apparently restored him to the chieftainship of the Trinovantes during the Roman invasion of Britain in 55 BC. However, when the Teutons under Arminius defeated the Romans in 9 AD, and caused the attention of the Roman military to be directed elsewhere, the Catuvellauni under their leader Cunobelinus --- Shakespeare's Cymbeline --- attacked the Trinovantes and captured Camulodunum.
The Trinovantes reappear in history when they participated in Boudicca's revolt against the Roman Empire in 60 AD. Their name, reshaped as Troi-novantes to mean "New Troy," is the source of Geoffrey of Monmouth's spurious claim that Celtic Britain was settled by Brutus of Britain and other refugees from the Trojan War.