According to some early medieval sources , the Siege of Exeter or Siege of Caer-Uisc was a military conflict Hostile_encounter that took place Process_start in or around 630 CE , between the Mercians , led by Penda of Mercia , and the Britons occupying Caer-Uisc ( Exeter ) in the kingdom of Dumnonia .

Penda is said Communication to have laid Placing siege to the town until the exiled British High King Cadwallon of Gwynedd , arrived Arriving to confront him .

An alliance between British and Mercian forces followed Motion , secured Assistance by Cadwallon 's marriage Forming_relationships to Alcfrith , Penda 's sister , and they marched Motion_directional north to face the armies of Northumbria ( who were occupying Gwynedd ) at the Battle of Cefn Digoll .

The Flores Historiarum ( mistakenly attributed to Matthew of Westminster ) recalls Statement that the Britons were still in possession of Exeter in 632 , when it was bravely defended Defending against Penda of Mercia until relieved by Cadwallon , who engaged Participation and defeated Hostile_encounter the Mercians with great slaughter .