Uniates are Eastern Christians in external communion with the see of Rome, and are most numerous in those provinces which formerly belonged to Poland. When Sigismund II was elected to the crown of Poland, being a zealous agent of the Jesuits, he at once took measures for reconciling the Polish Church to Rome. His plans were so successful that the archbishop of Kief summoned a synod at Brest, in Lithuania, to whom he presented the necessity and advantages of a union with Rome. The clergy favored the project, but it met with a strong opposition from the laity, and could not then be carried into effect. At a synod which met at the same place Dec. 2 1594, the archbishop and several bishops gave their assent to the scheme of union which had been proposed at the Council of Florence, thus recognizing the Filioque, or double procession of the Nicene Creed, and acknowledging the supremacy of the pope. They stood out, however, for retaining the use of the vernacular Slavonic in the celebration of divine service for the ritual and discipline of the Eastern Church. On the return. of the bishops sent to Rome to announce this event, the king, in 1596, convened the synod at Brest for the publication and introduction of the union. This was met by a public protest on the part of the opposite party, which repudiated the acts of the Uniates, and declared their unaltered attachment to the ancient Church of their country and to the patriarch of Constantinople. Sigismund deprived them of their churches and convents, and forbade the promulgation of Greek doctrines in his dominions. This division of the Church continued in full force until the partition of Poland, in 1772, at which time between two and three millions of the Uniates gave up their allegiance to Rome, and returned to the Eastern Church. In 1839 2,000,000 more were reconciled; but there are still about 300,000 in Russia and 3,000,000 in Austria. See Krasinski, Reform in Poland; Mouravief, Hist. o the Church of Russia; Neale, Patriarchate of Alexandria.