A church council held by Pope Urban II on 1-7 March 1095, at which appeals were made to the church of the West from the Byzantine Empire for military assistance against the onslaught of the Saljûq Turks.
By 1095, when he set out on a journey through Italy and France, Urban II had established his papal authority in much of Latin Christendom. In March 1095 at Piacenza, where he was to celebrate a council, he was approached by an embassy from the Byzantine emperor Alexios I Komnenos, who considered him the leader of the West. During the council Alexios’s legates entreated the pope to aid the Byzantine Empire against the Turks by sending troops. Unbelievers were threatening Constantinople, the emissaries claimed, and had devastated Christian churches throughout the East. The Byzantines themselves were unable to fend them off and needed Western assistance. The chronicler Bernold of Konstanz, who recorded the encounter, also stated that Urban had induced many to declare even under oath that they would go to Constantinople to assist Emperor Alexios most faithfully. The legislation from the council itself as far as preserved does not allude to the Byzantine entreaty.
The well-attended assembly had to meet outdoors at times, since no church at Piacenza was large enough to hold the numbers of those who had come to debate the problems of simony and of schismatically ordained clergy, burning issues in the north of Italy, where allegiance to the anti pope Clement III predominated. Urban was conciliatory toward some of the schismatically ordained clergy. If there were extenuating circumstances, they would be allowed to continue in their offices. The call for armed assistance for Christians in the East, for Jerusalem, and implicitly for Emperor Alexios had to wait until the Council of Clermont in November 1095.