Carsten Selch Jensen :
Towns and crusades in the Baltic during the early 13th century

Cities, towns and villages were essential to the crusaders in all the major crusading areas. These settlements of the frontier regions were at the same time strongholds, marketplaces and centres of administration, from which the ongoing crusades were organised and conducted. Troops were also recruited amongst the townspeople who were often obliged to serve as soldiers in the continuous fight between Christians and their enemies. This includes the cities and towns along the coast of the Baltic Sea. Papal privileges granted to these cities and the direct engagement of the townspeople in the ongoing crusades demonstrate this.
Thus the crusades in the Baltic did not only involve the traditional warrior class – the knights – but also the townspeople living on or nearby the frontiers of western Christendom. The crusades were an enterprise that influenced the whole of society in the regions subjected to crusading warfare – warriors and merchants alike. In fact it was hard to tell the difference when merchants and city-dwellers, through vows and privileges, turned into crusaders and left their towns and cities to fight alongside the crusaders, perhaps for the defence of their hometown but often also for the sake of their salvation.