History of Christianity
The schism became "official" in 1054 when the Pope's legates notified Patriarch Michael Cerularius of Constantinople that he had been excommunicated.  A few days later, he excommunicated the legates. Attempts at reconciliation were made in 1274 in Lyon and in 1439 in Basel, but in each case the eastern hierarchs who agreed to the unions were repudiated by the Orthodox as a whole.  However, reconciliation was achieved between the West and what are now called the "Eastern Rite Catholic Churches".  More recently, in 1965 the mutual excommunications were rescinded by the Pope and the Patriarch of Constantinople, though schism remains.