Gregorian Reform
On the eve of the Crusades, after a thousand years of reputedly uninterrupted succession of popes, the Papacy was Catholic Europe's oldest institution. The popes were seen as the Apostle Saint Peter's successors, and their prestige was high. In the west, the Gregorian Reform reduced lay influence on church life and strengthened papal authority over the clergy. Eastern Christians continued to consider the popes as no more than one of the five highest ranking church leaders, titled patriarchs, and rejected the idea of papal supremacy. This opposition, together with differences in theology and liturgy, caused acrimonious disputes which escalated when a papal legate excommunicated the Ecumenical Patriarch of Constantinople in 1054. The patriarchs of Alexandria, Antioch, and Jerusalem sided with the Ecumenical Patriarch against the Papacy, but the East–West Schism was not yet inevitable, and the Catholic and Orthodox Churches remained in full communion. The Gregorian Reform enhanced the popes' influence on secular matters. To achieve political goals, popes excommunicated their opponents, placed entire realms under interdict and promised spiritual rewards to those who took up arms for their cause. In 1074 Pope Gregory VII even considered leading a military campaign against the Turks who had attacked Byzantine territories in Anatolia.