Union of Brest

After Patriarch Jeremias II left Muscovy in 1589,[1] four out of nine bishops of the Eastern Orthodox Church in the Ruthenian lands of the Polish–Lithuanian Commonwealth gathered in synod in the city of Brest.

At the request of Prince Konstanty Wasyl Ostrogski, Hypatius Pociej left his post of Greater Castellan of Brześć Litewski and accepted the King's appointment to the eparchy of Volodymyr-Brest.

The bull recites the events which led to the union, the arrival of Pociej and Terlecki at Rome, their abjuration, and the concession to the Ruthenians that they should retain their own rite, save for such customs as were opposed to the purity of Catholic doctrine and incompatible with the communion of the Roman Church.

"[b] The bishops asked to be dispensed from the obligation of introducing the Gregorian Calendar, so as to avoid popular discontent and dissensions, and insisted that the king of Poland should grant them, as of right, the dignity of senators.

[5] The union was strongly supported by the King of Poland and Grand Duke of Lithuania, Sigismund III Vasa, but opposed by some bishops and prominent nobles of Rus', and (perhaps most importantly) by the nascent Cossack movement for Ukrainian self-rule.

[7][need quotation to verify] In 1620, the Metropolis of Kiev, Galicia and all Ruthenia was erected under the care of the Patriarchate of Constantinople for dissenting Eastern Orthodox faithful.