The Second Council of Nicaea was the seventh ecumenical council of Christianity; it met in 787 AD in Nicaea (site of the First Council of Nicaea; present-day İznik in Turkey) to restore the honoring of icons (or, holy images), which had been suppressed by imperial edict inside the Byzantine Empire during the reign of Leo III (717 - 741). His son, Constantine V (741 - 775), had held a synod to make the suppression official.
The veneration of icons had been finally abolished by the energetic measures of Constantine V and the Council of Hieria which had described itself as the seventh ecumenical council. These iconoclastic tendencies were shared by his son, Leo IV. After the latter's early death, his widow Irene, as regent for her son, began its restoration, moved thereto by personal inclination and political considerations.
When, in 784, the imperial secretary Patriarch Tarasius was appointed successor to the Patriarch Paul IV, he accepted on the condition that intercommunion with the other churches should be reestablished; that is, that the images should be restored. However, a council, claiming to be ecumenical, had abolished the veneration of icons, so another ecumenical council was necessary for its restoration. Pope Adrian I was invited to participate, and gladly accepted. However, the invitation intended for the oriental patriarchs could not even be delivered to them. The Roman legates were an archbishop and an abbot, each named Peter.
In 786, the council met in the Church of the Holy Apostles in Constantinople. However, soldiers in collusion with the opposition entered the church, and broke up the assembly. As a result, the government resorted to a stratagem. Under the pretext of a campaign, the iconoclastic bodyguard was sent away from the capital — disarmed and disbanded.
The council was again summoned to meet, this time in Nicaea, since Constantinople was still distrusted. The council assembled on September 24, 787. It numbered about 350 members; 308 bishops or their representatives signed. Tarasius presided, and seven sittings were held in Nicaea. Proof of the lawfulness of the veneration of icons was drawn from Exodus 25:17 sqq.; Numbers 7:89; Hebrews 9:1 sqq.; Ezekiel 41, and Genesis 31:34, but especially from a series of passages of the Church Fathers; the authority of the latter was decisive.
It was determined that "As the sacred and life-giving cross is everywhere set up as a symbol, so also should the images of Jesus Christ, the Virgin Mary, the holy angels, as well as those of the saints and other pious and holy men be embodied in the manufacture of sacred vessels, tapestries, vestments, etc., and exhibited on the walls of churches, in the homes, and in all conspicuous places, by the roadside and everywhere, to be revered by all who might see them. For the more they are contemplated, the more they move to fervent memory of their prototypes. Therefore, it is proper to accord to them a fervent and reverent adoration, not, however, the veritable worship which, according to our faith, belongs to the Divine Being alone — for the honor accorded to the image passes over to its prototype, and whoever adores the image adores in it the reality of what is there represented." St. Basil the Great The clear distinction between the adoration offered to God, and that accorded to the images may well be looked upon as a result of the iconoclastic reform. However sculpture in the round was condemned as "sensual". The twenty-two canons drawn up in Constantinople also served ecclesiastical reform. Careful maintenance of the ordinances of the earlier councils, knowledge of the scriptures on the part of the clergy, and care for Christian conduct are required, and the desire for a renewal of ecclesiastical life is awakened.
The papal legates voiced their approval of the restoration of the veneration of icons in no uncertain terms, and the patriarch sent a full account of the proceedings of the council to Pope Adrian I, who had it translated (the translation Anastasius later replaced with a better one).
This council is celebrated in the Eastern Orthodox Church as "The Sunday of the Triumph of Orthodoxy" each year on the first Sunday of Great Lent—the fast that leads up to Pascha (Easter)—and again on the Sunday closest to October 11 (the Sunday on or after October 8). The former celebration commemorates the council as the culmination of the Church's battles against heresy, while the latter commemorates the council itself.