The face of war changed across the period 1000-1300. By the latter date, armies usually had more and better iron weapons. Many had siege-trains with specialized equipment and an apparatus of supply. But armies remained ad hoc bodies, whose structures were dominated by the gradations of landowning society and its preoccupations. It was always difficult to sustain them in the field and even the greatest of forces could melt away. There was a new professionalism, but it made little impact on command and its effect was limited by the inability of states to sustain armies in being.
Although there is some evidence that they tended to get larger by the end of the thirteenth century, armies varied in size considerably across the period. A great event such as the Conquest of England in 1066 could arouse even a small state to enormous efforts: in 1066, the Normans mobilized 14,000, amongst them 6,000-7,000 fighting men. Robert Guiscard gathered 15,000 for his attack on the Byzantine Empire in 1081-5. The sources often exaggerate numbers: Barbarossa's army at the siege of Milan in 1158 is said by both versions of the annals of Milan to have numbered 15,000 knights and an untold number of foot - Otto of Freising suggests 100,000 and the Annales Sancti Disibodi offers 50,000. The fact that on this occasion Frederick was forced to come to terms with Milan suggests something less than any of these figures: a reasonable guess would be about 15,000. Frederick probably raised an army of about the same size for the siege of Crema, for this was an enormous effort and we know that the emperor was supported by a number of German princes, including Henry the Lion, as well as his Italian allies. But after the fall of Crema this army went home, and at the battle of Carcano on 9 August 1160 Barbarossa could muster only some 400 cavalry and 2,500-3,000 foot. By May 1161, when Frederick moved to the siege of Milan, he had been reinforced, but still had only 2,100 German knights, with substantial