The Seventh Ecumenical Council (787)
Tarasius made the convening of an ecumenical council the central condition of accepting the patriarchate. Working with Empress Irene, he secured the participation of Pope Adrian I through correspondence and sought the involvement of the Eastern patriarchates. An initial attempt to gather the council in Constantinople in 786 collapsed when mutinous soldiers dispersed the assembled delegates.
The council reconvened at Nicaea in September 787, with Tarasius presiding and, by the tradition, 367 bishops in attendance. It condemned iconoclasm and formally affirmed the veneration of the holy icons, distinguishing such veneration from the worship due to God alone, and it received repentant former iconoclasts back into the Church. Tarasius's lenient policy toward those who had previously embraced iconoclasm drew criticism from stricter monastic circles, including the monk Theodore the Studite.