In southern England the danegeld was based on hidages, an area of agricultural land sufficient to support a family, with the exception of Kent, where the unit was a sulung of four yokes, the amount of land that could be ploughed in a season by a team of oxen; in the north the typical unit was the carucate, or ploughland, equivalent to Kent's sulung; and East Anglia was assessed by the hundred. Everywhere the tax was farmed (collected) by local sheriffs. Records of assessment and income pre-date the Norman conquest, indicating a system which James Campbell describes as "old, but not unchanging". According to David Bates, it was "a national tax of a kind unknown in western Europe"; indeed, asserts that the national system of land taxation developed to raise the Danegeld was the first to reappear in Western Europe since the collapse of the Western Roman Empire. It was used by William the Conqueror as the principal tool for underwriting continental wars, as well as providing for royal appetites and the costs of conquest, rather than for buying-off the Viking menace. He and his successors levied the geld more frequently than the Anglo-Saxon kings, and at higher rates; the six-shilling geld of 1084 is infamous, and the geld in Ely of 1096, for example, was double its normal rate. Judith Green states that from 1110, war and the "White Ship" calamity led to further increases in taxation efforts. By 1130 Henry I was taxing the danegeld annually, at two shillings on the hide. That year, according to the chronicle of John of Worcester the king promised to suspend the danegeld for seven years, a promise renewed by Stephen at his coronation but which was afterwards broken. Henry II revived the danegeld in 1155–1156, but 1161–1162 marks the last year the danegeld was recorded on a pipe roll, and the tax fell into disuse.