The Metropolitan of Kyivs of the second half of the 4th century were supporters of the Florentine Union of 1439 on the unification of the Catholic and Eastern Orthodox Churches and maintained ties with the Popes, as evidenced, in particular, by the letter of Bishop Mysail elected to the Metropolitanate of Kyiv to Pope Sixtus IV in 1476. and a letter from Metropolitan Joseph Bolgarinovych from 1500 to Pope Alexander VI. Subsequently, these relations were interrupted due to the intervention of the Ecumenical Patriarchate. In 1443, the Florentine Union was condemned by the Orthodox Churches (Patriarchate of Alexandria, Patriarchate of Antioch and Patriarchate of Jerusalem) at the Cathedral of Jerusalem. These events caused a crisis in the Metropolitanate of Kyiv.