The Celtic tribes in Briton resisted Roman advances through fighting, treaties, and some submission. The Iceni formed an alliance with Rome but were still under Roman control. When King Prasutagus of the Iceni died, his daughters were assaulted and Boudicca led the Iceni and other Celtic tribes in rebellion against Rome to liberate Britain. The tribes prepared for war while the Romans destroyed Druid sacred sites. Boudicca ambushed Roman forces and burned Roman settlements like Londinium. The Romans chose a battlefield and defeated the Britons, who were crushed with many casualties. Boudicca is believed to have poisoned herself after the rebellion failed against the more advanced Roman army.