Boudicca and the Iceni were not alone in their rampage across the island of Britain; they were joined in force by the tribe immediately south, the Trinovantes. The reasons for the Iceni rebellion are known, however nobody is entirely sure why this neighbouring tribe became so intimately involved in the battle.
The most probable reason is a basic, predisposed resentment towards the Romans. Not only were the indigenous people subject to Roman taxation, but they were being driven off their land and delegated to a life of slavery. Adding to this chronic resentment was the erecting of the Temple of Claudius in Colchester, which served as a reminder of Roman ill deeds and immediately became an object of derision for the Britons.
It was in 60 CE that Seutonius Paulinus, the Roman governor, decided to set his sights on the tiny island of Mona off the northern shore. Mona was the island of the Druids and the center of Celtic nationalism. It was at this time that the Iceni and the Trinovantes, protected by water or dense forest on all sides, joined forces and decided to head north to meet the Roman army. While the Romans saw a profitable gain approaching with the taking of Mona, they failed to realize that what was sneaking up behind them was what they feared most: a confederacy of "barbarians".