spiritual sword wielded by the heir to St Peter was superior to the temporal weapons at the disposal of the emperor, then the whole basis of imperial power, especially imperial claims to the secular leadership of Europe, came into question. Both sides turned to the 'new men' of the twelfth-century schools to provide them with manpower and ammunition for a debate which was to continue throughout the Middle Ages. At the same time that courts throughout western Europe were developing improved systems of administration, so too the papal curia attracted to its service able clerics to process the increasing amount of business--judicial appeals, complaints, questions of morality, and, increasingly, the organization of crusades-which poured into Rome in the twelfth century. Tradition, always one of the strongest weapons at the disposal of a papacy which increasingly emphasized the Petrine claim and used the talents of men such as Gratian, the celebrated canon lawyer, to delve back into the papal archives to rediscover the forgotten rights of the pope, was also called upon by the defenders of imperial rights. For them, the justification for imperial intervention in Italy rested on the rock of Roman Law, for it was precisely in the Justinianic corpus that the unchallenged rights of the emperor to superiority in secular matters in the empire and guardianship of the Church were most clearly stated. The schools of Bologna, famous in the twelfth century for their training in law, produced men who could argue the case both for papal supremacy and for the theoretical strength of the imperial position.
It was, therefore, with renewed confidence that the Emperor Frederick I Barbarossa invaded Italy for the first time in 1154. In the next thirty years, until peace was made at Constance in 1183, he led numerous expeditions against both the pope and the towns of Italy and amidst the complexities of this period of alarmingly confused alliances, the principles behind his intervention do emerge. One could be seen in his response to the appeals made to him by smaller towns in Lombardy (such as Lodi) which resented the growing power of Milan. It was in the old guise of imperial overlord that he promised to restore justice and the old peace of the empire. In return, the
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