Walcher, the Bishop of Durham and Earl of Northumbria. Walcher was killed on 14 May 1080, and the king dispatched his half-brother Odo to deal with the rebellion. William departed Normandy in July 1080, and in the autumn his son Robert was sent on a campaign against the Scots. Robert raided into Lothian and forced Malcolm to agree to terms, building a fortification (the 'new castle') at Newcastle upon Tyne while returning to England. The king was at Gloucester for Christmas 1080 and at Winchester for Whitsun in 1081, ceremonially wearing his crown on both occasions. A papal embassy arrived in England during this period, asking that William do fealty for England to the papacy, a request that he rejected. William also visited Wales in 1081, although the English and the Welsh sources differ on the exact purpose of the visit. The Anglo-Saxon Chronicle states that it was a military campaign, but Welsh sources record it as a pilgrimage to St Davids in honour of Saint David. William's biographer David Bates argues that the former explanation is more likely, explaining that the balance of power had recently shifted in Wales and that William would have wished to take advantage of the changed circumstances to extend Norman power. By the end of 1081, William was back on the continent, dealing with disturbances in Maine. Although he led an expedition into Maine, the result was instead a negotiated settlement arranged by a papal legate. Last years Sources for William's actions between 1082 and 1084 are meagre. According to the historian David Bates, this probably means that little happened of note, and that because William was on the continent, there was nothing for the Anglo-Saxon Chronicle to record. In 1082 William ordered the arrest of his half-brother Odo. The exact reasons are unclear, as no contemporary author recorded what caused the quarrel between the half-brothers. Orderic Vitalis later recorded that Odo had aspirations to become pope. Orderic also related that Odo had attempted to persuade some of William's vassals to join Odo in an invasion of southern Italy. This would have been considered tampering with the king's authority over his vassals, which William would not have tolerated. Although Odo remained in confinement for the rest of William's reign, his lands were not confiscated. More difficulties struck in 1083, when William's son Robert rebelled once more with support from the French king. A further