Byzantine iconoclasm, the rejection of religious images as a form of idolatry, had already been condemned once, at the Second Council of Nicaea in 787, only to be revived by later emperors who again ordered icons removed from churches and their defenders persecuted. Emperor Theophilos, an active iconoclast, died in 842 leaving the throne to his infant son Michael III, with Theophilos's widow Theodora ruling as regent. Theodora, who had reportedly continued to venerate icons privately even during her husband's reign despite the risk of doing so, moved quickly to reverse imperial policy once she held power in her own right.
She convened a synod at Constantinople in March 843 that deposed the sitting iconoclast patriarch, restored the pro-icon Methodios to the patriarchate, and formally reaffirmed the teaching of the Second Council of Nicaea that icons could be venerated without idolatry, since the honor shown to an image passes to what it represents rather than terminating in the material object itself. The synod's decision was announced on the first Sunday of Great Lent, and Orthodox churches have kept that day as a feast of the restoration ever since. Theodora is venerated in the Orthodox Church as a saint in her own right, remembered specifically for this act, and the feast she set in motion has outlasted every other episode of the century long iconoclast dispute in continuous liturgical memory.