WILLIAM IS NOT usually thought of as a historian of crusading, nor much referred to by modern historians of the phenomenon. His most famous work, the Gesta Regum Anglorum, is primarily what its title suggests. But, as we have seen, there are many digressions, mostly into continental history. William was conscious of them and justified them in explicit appeals to the reader. Some provide necessary background to the course of English affairs, some are there for their entertainment value, and some because of their intrinsic importance in the general course of European history. One of these digressions is his account of the First Crusade, and it comes into the third category. It is the longest of all the diversions, occupying the last forty-six of the eighty-four chapters which make up Book IV, or about 12 per cent of the complete work. This is as long as a number of independent chronicles of the First Crusade (such as Fulcher of Chartres’ Gesta Francorum Iherosolimitanum Peregrinantium in its earliest version, or the anonymous Gesta Francorum), and the story is brilliantly told. It follows the course of the Crusade from the Council of Clermont to the capture of Jerusalem, continuing with the so-called Crusade of 1101, and the deeds of the kings of Jerusalem and other great magnates such as Godfrey of Lorraine, Bohemond of Antioch, Raymond of Toulouse and Robert Curthose. The detailed narrative concludes in 1102; some scattered notices come down to c.1124, close to the ‘publication’ of the Gesta, with a very little updating carried out in 1134–5. Separately, in (Book V) c. 410, again as a digression, William briefly recounts the crusading expedition of King Sigurd of Norway (1107–11), although in that instance he is more concerned with the extraordinary events which accompanied the king's outward and homeward journeys than with what (little) he did in the East.

The digression on Crusade was considered and planned; it is to that extent integral to the structure of the Gesta Regum. The prologue to Book IV announces that its subject will be the reign of William II and