"Following Lourens and Lucassen, craft guilds are defined here as ‘‘organizations that – with the agreement of the local authority – unite members of the same occupational group, with as their most important goal the furthering of their economic interests, but not without taking into account the general well-being of their group as well’’. Due to a lack of sources, it is often impossible to discover whether late medieval guilds would have corresponded entirely to that definition from their first foundation, and they might indeed have developed from relatively informal institutions eventually to be recognized by local authorities. Guilds were mainly urban institutions, but in some cases the densely populated setting in which they developed had, even so, not yet been awarded the legal title of ‘‘city’’." (https://www.ris.uu.nl/ws/files/20096187/_PUB_SilentRevolution_IRSH_53_Suppl.pdf)
"Given the urban character of guilds, it is quite natural then that we should see their origins in relation to the process of urbanization that occurred in western Europe between 900 and 1300. One of the prerequisites for the emergence of guilds is a certain concentration of members of the same occupational group in the same location.
If we consider the Netherlands, Lourens and Lucassen claim that in about 1400 a city needed to have reached a population of at least 2,500 inhabitants before more than a single craft guild would become established, so that small towns of fewer than 500 inhabitants could not usually support craft guilds. Although there are exceptions to their rule, there did seem to be a certain population threshold for guilds to be able to develop. There was, too, an upper limit to the number of guilds per urban centre, with an apparent maximum of about 50 guilds per city. Cities such as Amsterdam, with a much larger than average population, had only a single guild per 4,000 inhabitants (1670: 52 craft guilds per 200,000 inhabitants), but, as a form of compensation perhaps, each of those organizations included on average many more members.
The literature offers two interpretations of the rise of merchant and craft guilds in the centuries between 950 and 1300. The first constructs a link with the collegia developed during the Roman period; these protoguilds disappeared in western Europe, whereas they continued to be important in Byzantium, although by the thirteenth century they had gradually disintegrated there too.35 Most of them were, like the Roman collegia, closely supervised and monitored by the state, which contributed to undermining the ‘‘serviceability of the guild system’’.
The model spread to western Europe via southern Italy, through the Byzantine link to Amalfi in the tenth century, typically mentioned as the first site of a ‘‘modern’’ merchant guild. Hickson and Thompson describe how the ‘‘guild model’’ reached French and Flemish cities from the south, where the merchants with whom the Italians traded at the Champagne fairs lived, followed by a spread to western Germany and England in the twelfth century, to Spanish trading centres around the middle of the thirteenth century onward, and in the late thirteenth and fourteenth centuries to the East.
The alternative view contends that guilds developed from informal groups of merchants – or indeed other social groups – who in northwestern Europe organized themselves spontaneously in the ninth and tenth centuries, the first examples being Saxon gegildan known from tenth-century England,38 or the famous Frisian merchant guild from Tiel, known from an early eleventh-century reference by Alpertus van Metz. That body settled disputes between merchants, arranged for the mutual exchange of credit, and organized the obligatory drinking and feasting." (https://www.ris.uu.nl/ws/files/20096187/_PUB_SilentRevolution_IRSH_53_Suppl.pdf)