A recommendation to summon an ecumenical council, in order to correct the iconoclast heretics, had been addressed to Empress Irene, then acting as regent for her son Emperor Constantine VI (780-797) who was still a minor. The aim was to unite the church and to condemn the decrees passed by the council of 338 bishops held at Hiereia and St Mary of Blachernae in 754.
Second Council of Nicaea
The gathering together of the council was announced to Pope Hadrian I (772-795) in a letter of Constantine VI and Irene, dated 29 August 784. Pope Hadrian I was urged to attend in person or to send his personal representative. Patriarch Tarasius sent the same message in synodal letters to the pope and the three eastern patriarchs. Pope Hadrian I for the gathering of the council and sent his representatives archpriest Peter and Peter the abbot of the Greek monastery of St. Sabas in Rome. The council met for the first time on 1 August 786, in the presence of Emperor Constantine and Empress Irene. When the proceedings were interrupted by the violent entry of iconoclast soldiers, faithful to the memory of Emperor Constantine V (741-775), the council was adjourned until the arrival of a reliable army under Staurakios. It assembled again at Nicaea on 24 September 787.
After the bishops suspected of heresy had been admitted, 263 fathers embraced the doctrine concerning the cult of sacred images as explained in the letters of Pope Hadrian I, which were read out at the second session. The question of the intercession of saints was dealt with in the fourth session. After all these matters had been approved in the seventh session, a doctrinal definition was decreed. At the eighth and last session, which was held at the request of Constantine and Irene in the Magnaura palace in Constantinople, the definition was again decreed and proclaimed and 22 canons were read out. The papal representatives presided over the council and were the first to sign the acts; but in reality it was Patriarch Tarasius who presided, and it was he who informed Pope Hadrian I about it. Pope Hadrian I wrote no letter in reply, yet the defence he made of the council in 794 against Charlemagne shows that he accepted what the council had decreed, and that he had sent no acknowledgement because the concessions which he had requested to Constantine and Irene had not been granted to him, especially concerning the restoration of the papacy's patrimony to the state at which it had been prior to 731. Emperor Constantine VI and his mother Irene signed the acts of the council but it is unclear whether or not they promulgated a decree on the matter.
The Nicene Creed: