In May 1147, people from across southern and eastern England gathered at the port of Dartmouth, where they took an oath. Joining forces with fleets from the Rhineland and Flanders, they sailed to besiege Lisbon, at this time under Muslim rule. Their assault, co-ordinated with the king of Portugal, eventually succeeded, and they took the city – one of the few successes of the generally disastrous Second Crusade.

It may appear idiosyncratic to begin an exploration of urban populations and associations with this incident of crusading history. But it actually takes us to the issue's heart: for although from one perspective this was the work of an association of crusaders, from another it resembles nothing so much as the activities of a specially formed urban community, a town afloat. This is partly because the group consisted largely of townspeople from coastal towns including Ipswich, Southampton, Bristol and Hastings, together with representatives from Cologne and other North Sea towns – a salutary reminder that urban communities were never extrinsic to the rest of society, and that people in towns were caught up in just the same currents of history as everyone else, including the crusading movement. But more importantly, the group acted as townsmen tended to act. In the absence of pre-arranged or self-evident aristocratic leadership, a collective oath was sworn, creating an artificial community resembling those formally recorded in town archives.