"The most thorough discussion of the number of combatants on the First Crusade is that offered by John France and this study cannot improve on his painstaking assembly of the relevant data and the plausible manner in which it assessed. At its height, gathered together at Nicea, John France estimates the Christian army to have been composed of some 50,000 combatants, of whom 7,000 were knights. Using these figures as a guide, the overall composition of the crusade would have, very approximately, been as follows. Nine princes, 200 magnates, 7,000 knights, 40,000 footsoldiers, and 40,000 pauperes.
This overall figure of around 90,000 people differs from France’s estimate of 50–60,000 inclusive of non-combatants and it is at the high end of estimates by other modern historians, even though most have revised upwards the estimate in Steven Runciman’s discussion of the subject, that there were 4200 to 4500 cavalry and 30,000 infantry.
Jonathan Phillips offers the figure of 60,000, although somewhat confusingly these are divided between 6,000 knights and the rest ‘servants, pilgrims and hangers-on.’ In other words, the footsoldiers are absent. (...)
The huge variation of the various estimates is a fair reflection of the difficulty of the sources in regard to the reporting of numbers and this study claims no great authority on the matter. It does seem inconsistent of France, though, to assess the number of combatants of the First Crusade at 50,000, yet the overall number, including non-combatants, at 50–60,000. The discussion in Chapter Three shows that when the People’s Crusade departed and, indeed, the various contingents of the princes, the movement had something of a mass emigratory character.
The People’s Crusade was overwhelmingly made up of pauperes, but they were also present in substantial numbers among those marching with the princes. Even after the destruction of the People’s Crusade, thousands of survivors (and later, returned prisoners) joined up with the united army.
That is why it seems reasonable to push the overall figure for the expedition to the higher one of 90,000 by including some 40,000 non-combatants with the 50,000 soldiers."
This blog quotes an abreviated section of the book The Social Structure of the First Crusade by Conor Kostick (2008), which is available at Brill Leiden/Boston via http://bit.ly/2UkqvRF. This is an open access title distributed under the terms of the cc-by-nc License, which permits any non-commercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. Illustration shows The siege of Jeriusalem at 1099, Source Wikimedia Commons