From 43 CE onward Rome had gradually taken over the southeast of Britain.
Some British kingdoms were conquered, others became vassals or allies.
The king of the Iceni tribe, located in modern Norfolk, had promised his lands to a union of his daughters and the Roman emperor Nero after his death.
But when he died, the Romans seized everything, flogged his widow Boudica and raped his daughters.
The Iceni were outraged and as soon as the Roman legions were campaigning elsewhere (in the north), they rebelled.
They made a surprise attack on Camulodunum (Colchester, the provincial capital), slaughtering Romans and Roman 'collaborators' and then torched the town.
Half the of the Roman 9th legion was sent to rescue the civilians, but they were ambushed and routed by Boudica's army.
Next targets were Londinium (London) and Verulamium (St. Albans), where they also killed Romans and destroyed Roman buildings wherever they found them.
In the meanwhile the Roman Governor of Britain, Gaius Suetonius Paulinus, had raced back to the south with his army.
He was outnumbered and abandoned Londinium, but eventually had to do battle to stop the revolt.
The battle probably took place between Londinium and Viroconium (Wroxeter), near the Roman road that is now known as Watling Street.
Suetonius had his 14th legion with him, parts of the 20th legion and auxiliaries, in all 5,000 legionaries, 4,000 auxiliaries and 1,000 cavalry.
The size of Boudica's army is vague and obscured because several estimates also included family members who came to watch the battle from close by, expecting another easy victory after Camulodunum.
She probably had 40,000 - 80,000 warriors and a number of chariots.
Suetonius chose his position carefully in a narrow gorge, protected on three sides by forest.
Boudica led her army into attack, but soon the large numbers got compressed in the narrow gorge.
Starting at 40 meters there were met by a double hail of pila, which took out many of the most experienced Britons, who fought in the front ranks.
After this the Romans advanced in a line of small wedges, which further distorted the British formation and pressed the Britons onto each other.
Formation, height advantage, armor, experience and desperation gave the Romans a decisive edge and they inflicted heavy losses on their enemy.
The Britons started to fall back, but were attacked by Roman cavalry on the flanks and hampered by wagons and supporters in the rear.
The result was a rout and a slaughter.
British losses were several tens of thousands, including families, but only 400 - 500 for the Romans.
The defeat of the Iceni broke resistance to Roman rule.
Queen Boudica is said to have taken poison afterwards, though others claim she fell in the battle.
Nero replaced Suetonius because he feared that the man had gained a too fearsome reputation.
War Matrix - Battle of Watling Street
Roman Ascent 200 BCE - 120 CE, Battles and sieges