Since Julius Caesar's invasion of Brittania in 55 BC had failed, no Roman Emperor had set foot on the British island. But when Claudius became Emperor in 41 AD, he thought it would be worth the try, and invaded Britannia again. He had more success: the eastern part of the island was set under Roman control in 43 AD. Many Celtic tribes voluntarily allied with the Romans in trade of their safekeeping. So did the Iceni, of which Prasutagus was chieftain (or king, as the leaders of tribes used to call him themselves), and Boudica was queen. Claudius had fortresses built and troops installed in several places in eastern Brittania, and a Roman governor was appointed to keep an eye on the Celts.
The second Roman governor, Publius Ostorius Scapula, took all weapons from the tribes that he didn't trust completely, like the Iceni, even if they had surrendered. This was a smart move, since he initiated a couple of things that would highly upset the Celts. For example, in 49 AD, he set up a colonia around Camulodunum (now Colchester): a town that would serve as a homestead for Roman veterans. Because the colonia grew fast and the Britons were driven off their land to make way for the veteran homes. Several were enslaved by the retired legionaries, others were executed.
In 54 AD (Ostorius had died and had been succeeded by a less provoking administrator), Emperor Claudius was poisoned and Nero followed him on the throne. Nero ordered to build a temple to his predecessor at Camulodunum. Now the tribal people were obliged to pay for a place of worship for a man who had took their lands! And on top of that, Rome demanded a repayment of money that had been loaned to chieftains that weren't even alive anymore.
Four years later, in 58, Gaius Suetonius Paulinus became governor of Britain, and he had the same aggressive manner as Ostorius. He strived to annex the western parts of Britannia, and set out for a campaign. In 60 AD, a 10,000 men strong Roman army set over from the mainland, committed to 'kill all savages' under guidance of Suetonius. The troops invaded the stronghold of druids on the island of Mona, massacred the people and burned down their sacred groves.
In that same year, king Prasutagus of the Iceni died. He had appointed the Emperor as his co-heir, together with Boudica and their daughters. By adopting Nero in his will, he was probably hoping that his will would be carried out. But the Romans only acknowledged inheritance through the male line and saw the chance to annex the tribe, so they ignored Prasutagus's testament. His legacy and the Iceni tribe now belonged to Rome. Rome's financial officer, Decianus Catus, soon visited Boudica to take an inventory of what was Roman property in his opinion. Boudica objected stating she was the queen of an independent tribe, but the Romans, for whom women had no meaning at all, silenced her by whipping her in front of her people. If that wasn't demoralizing enough, the soldiers took and raped her daughters and plundered the houses. The Romans left a mess and a clear message: the Iceni would have to obey them.
Boudica, however, wasn't planning on accepting this. She was determined to take revenge and to stop the Roman tyranny over her people. Although Ostorius had disarmed them officially, they had secretly stockpiled weapons. Boudica conspired with several neighboring tribes to revolt against the Romans and Boudica was chosen to be the leader of this revolt. Men and women, elderly and infants, were willing to fight against the army that had humiliated them so badly, and soon Boudica found herself heading an army of 120,000 people. There were soldiers among them, but also priests, women and children. Instead of armors, they wore tattoos that were believed to confer magical powers. The Celtic army first moved against Camulodunum. Their arrival shocked the veterans settled there, who hadn't even built a wall around the city. They sent for military help from legions settled in Londinium, Longthorpe and Mona. From Londinium arrived a group of 200 men who weren't armed well. Boudica's army overran Camulodunum and defeated it within two days.
General Cerialis of the Ninth Hispanic Legion set for Camulodunum with an infantry of 2,000 and a cavalry of 500 men. He met Boudica before he could reach the town, and after Boudica had slaughtered the walking troops, Cerialis fled with his cavalry. Now Suetonius got wind of the uprising in the East, and headed eastward to meet Boudica in Londinium. Londinium - now London - was barely 15 years old and unwalled. It was clear at once that the town could not be saved; and Suetonius decided to sacrifice the town to await Boudica's army for a battle at a more strategic position. While Boudica wrecked Londinium (the first and only time London would be completely destroyed!), Suetonius gathered an army around him consisting of nearly 10,000 soldiers. Boudica's army, however, greatly outnumbered his - Cassius Dio writes in his Roman History that she had 230,000 men behind her by that time. But those were untrained and poorly armed people, and many of them were women. Furthermore, the Romans fought with short swords that were perfect for stabbing in close-range fights, whereas the Britons had long swords which were hardly of use when the Romans got near. Also, Suetonius chose a narrow valley as a battleground, in which the Britons could not come forward well, even less when the Romans approached in a v-formed formation. The Romans won victoriously, and the uprising was over.
It is uncertain if Boudica poisoned herself after losing that battle. Tacitus writes so, but this detail was first added twenty years after the original publication of the story. It may just have been his way to add more drama to it all, but it isn't hard to imagine how she must have felt on her dying bed. But time passed, and other governors came who strived for peace with the Britons. Boudica could not experience it herself, but eventually her people got the respect she had fought for.