After William became King of England, FitzOsbern was made an earl, with major land holdings in Gloucestershire, Herefordshire, Oxfordshire, and the Isle of Wight, and smaller areas under his authority in Berkshire, Dorset, Wiltshire, and Worcestershire. In the summer of 1067 King William returned to Normandy and left his half-brother Bishop
Odo of Bayeux and FitzOsbern in charge of England during his absence. The king was back in England in 1068 and FitzOsbern accompanied him in the subjugation of south-west England. He attended the King's
Whitsun court in May 1068, and then visited
Normandy, where he fell ill for some months. In February or March 1069 FitzOsbern was asked by William to oversee the peace in
York, where Gilbert de Ghent was made castellan of the new castle, but FitzOsbern returned south in time to attend the King's Easter court in April 1069 before returning to York.
Eadric the Wild launched a campaign of
Anglo-Saxon resistance in the
West Midlands, with the assistance of a number of Welsh princes (who had lately been allies of the Anglo-Saxon kings). In 1069 the revolt was crushed, and it is likely FitzOsbern played a major part in this, although the details are not certain. During this time FitzOsbern and his followers pushed on westwards into
Wales, thus beginning the Norman conquest of the Welsh
Kingdom of Gwent.
Castle builder As part of the assertion of Norman control over England and Wales, FitzOsbern was one of the major Norman
castle builders. Early castles attributed to him include
Carisbrooke Castle on the
Isle of Wight,
Chepstow Castle (
Striguil) in
South Wales,
Snodhill Castle,
Wigmore Castle and
Clifford Castle in Herefordshire,
Berkeley Castle in Gloucestershire and
Monmouth Castle in Wales. FitzOsbern also created or improved
fortifications in the towns of
Hereford and
Shrewsbury.
Distraction and death in Flanders In 1070 trouble arose in
Flanders, where King William's brother-in-law Count
Baldwin VI of Flanders had died, leaving his county and his young sons in the hands of his widow
Richilde, Countess of Mons and Hainaut. Her control of Flanders was challenged by the brother of her late husband,
Robert the Frisian. Looking for help, she offered herself in marriage to FitzOsbern. He could not resist the chance to become also Count of this rich principality close to Normandy, and hurried there with his army. However, he was defeated by the Count of Flanders and killed in the
Battle of Cassel on 22 February 1071. ==Marriages and children==