Another UNESCO report more specifically explains the need for a castle at this location:"In defensive terms, Durham Castle was of strategic importance both to defend the troublesome border with Scotland and to control local English rebellions, which were common in the years immediately following the Norman Conquest, and led to the so-called Harrying of the North by William the Conqueror in 1069. ... the Castle was constructed 'to keep the bishop and his household safe from the attacks of assailants'. This makes sense – Robert de Comines (or Cumin), the first earl of Northumberland appointed by William the Conqueror, was brutally murdered along with his entourage in 1069".