The classic theory of feudal beginnings is that put forth by Heinrich Brunner in 1887. Though Brunner's conclusions have been modified both by the arguments of his critics and by the insights of his defenders, the broad outlines of his theory are still widely accepted. Although Brunner's arguments that the war against the Muslims inspired Charles's revolution in military tactics and organization have been found wanting, the classic theory has been given new impetus by Lynn T. White, Jr., who has suggested an even more imaginative cause for the feudalization of Francia. The slow and gradual emphasis of pedetemptim is an accurate description of the tactical demands of the situation; tactically pedetemptim fits the context. Soon after becoming King, Pepin resumed his military activities. He sent a force to invest the fortified city of Narbonne in 752. The following year he invaded Saxony and attacked a castrum on Mt. Iuberg.