Another great evil which rivalled the plague as a curse, was the host of mercenary soldiers who swarmed over Italy like locusts. In the days of Barbarossa, battles like that of Legnano had been fought between the train-bands of the communes on one side and the feudal chivalry and men-at-arms on the other. But since then a great change had come over the methods of raising soldiers. Under the feudal system the term of service in the field for the liegemen of the Emperor had been forty days; but that time was too short for an effective campaign. When the Emperor wished to cross the Alps and go to Rome in order to receive the Imperial crown, he was obliged to hire soldiers; and, as years went on and these Imperial descents became mere adventurous expeditions, the character of the soldiers degenerated, until in Petrarch's time the Imperial armies were made up of ruffians recruited anywhere. There were also other reasons for establishing mercenaries in place of militia. The despots of Northern Italy did not wish their subjects trained to arms. The burghers of mercantile cities did not wish to leave their counting-rooms, nor to have their employees mustered out, so they too preferred hired soldiers to a native militia. Moreover, warfare had changed; cavalry needed frequent manoeuvres, bowmen and pikemen required drill and continuous discipline. Thus the old train-band system of the communes, under which the militia hurried to their appointed posts on the ringing of the bells, gave way to the system of mercenary troops led by soldiers of fortune, _condottieri_, as the Italians call them.