Under the influence of the Ottoman government, patriarch Symeon I convenes a synod of the Eastern Orthodox Churches in Constantinople. The council defines the ritual for admitting Catholics to the Eastern Orthodox Churches and condemns the church union of Ferrara-Florence.

Symeon I of Constantinople was Ecumenical Patriarch of Constantinople three times: for a short time in 1466, from 1471 to 1475 and from 1482 to 1486. In 1484 he presided over the Synod of Constantinople of 1484 which repudiated the Council of Florence.

The Synod of Constantinople in 1484 was an Ecumenical synod of the Eastern Orthodox Church that took place from 1 September 1483 to 31 August 1484. It was the first synod to condemn the Council of Florence and defined the ritual for reception of Catholics to Greek Orthodoxy.

The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is one of the three major doctrinal and jurisdictional groups of Christianity, with approximately 230 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the pope of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares, a title held by the patriarch of Rome prior to 1054. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe. Since 2018, there has been an ongoing schism between Constantinople and Moscow, with the two not in full communion with each other.

The Council of Florence is the seventeenth ecumenical council recognized by the Catholic Church, held between 1431 and 1445. It was convened in territories under the Holy Roman Empire. Italy became a venue of a Catholic ecumenical council after a gap of about 2 centuries. It was convoked in Basel as the Council of Basel by Pope Martin V shortly before his death in February 1431 and took place in the context of the Hussite Wars in Bohemia and the rise of the Ottoman Empire. At stake was the greater conflict between the conciliar movement and the principle of papal supremacy.