Fourth Council of Constantinople (Roman Catholic)

The Fourth Council of Constantinople (Roman Catholic) was the eighth Catholic Ecumenical Council held in Constantinople from October 5, 869, to February 28, 870. It included 102 bishops, three papal legates, and four patriarchs. The Council met in ten sessions from October 869 to February 870 and issued 27 canons.

The council was called by Emperor Basil I the Macedonian and Pope Adrian II. It deposed Photios, a layman who had been appointed as Patriarch of Constantinople, and reinstated his predecessor Ignatius.

The Council also reaffirmed the decisions of the Second Council of Nicaea in support of icons and holy images and required the image of Christ to have veneration equal with that of the gospel book.

A later council, the Greek Fourth Council of Constantinople, was held after Photios had been reinstated on the order of the emperor. Today, the Roman Catholic Church recognizes the council in 869–870 as "Constantinople IV", while the Eastern Orthodox Churches recognize the councils in 879–880 as "Constantinople IV" and revere Photios as a saint. At the time that these councils were being held, this division was not yet clear. These two councils represent a growing divide between East and West. The previous seven ecumenical councils are recognized as ecumenical and authoritative by both Eastern Orthodox and Catholic Christians. These kinds of differences led eventually to the East-West Schism of 1054.

With the coronation of Charlemagne by Pope Leo III in 800, the papacy had acquired a new protector in the West. This freed the pontiffs to some degree from the power of the emperor in Constantinople but it also led to a schism, because the emperors and patriarchs of Constantinople interpreted themselves as the true descendants of the Roman Empire.