Henry III ruled England for fifty-six years, a record broken only by George III, Victoria and Elizabeth II. Unlike George III or Victoria, who spent their final decades in retirement or decay, Henry remained publicly active until his death in 1272. Unlike the current sovereign, he not only reigned but ruled. It was he who commanded the nation in arms, he who negotiated taxes, and he whose tastes in art and architecture were permanently memorialised, most famously in his rebuilding of Westminster Abbey. Henry’s reign witnessed momentous events: war against France and Navarre, English bids to acquire the thrones of both Sicily and the Holy Roman Empire, at least three major baronial rebellions and, from the 1250s onwards, the emergence of Parliament, first as a tool of royal policy but later as a counterweight to Henry’s ineptitude. The scale of such events is matched by their massive archival legacy: their historian must contend with several thousand pages of government records, besides a wealth of other writings and artefacts scattered from Spain to the eastern Mediterranean.