The Theodore Psalter (London, British Library, Add. MS 19352) is a profusely illustrated Book of Psalms from 1066 and is possibly the most significant surviving manuscript illuminated in Constantinople. It was made at a time when the anti-image movement of the iconoclasts had relatively recently been beaten down, and representational art could again flourish. The name comes from the monk who illustrated the manuscript.
The Theodore Psalter illustrates important episodes and individuals from the great dispute over the role of images in Christian worship that had split the Church. It was made for Abbot Michael of the Studios Monastery, and is named after its scribe and illuminator, the monk Theodore, who came to Studios from Caesarea in Cappadocia. Working closely with the abbot, Theodore produced 435 marginal illustrations that act as a commentary on the text of the Psalms.
The earliest known image of the Three Hierarchs (Basil the Great, John Chrysostom and Gregory the Theologian) together comes from a miniature in the Theodore Psalter dated to 1066. This is significant because the Feast of the Three Hierarchs was instituted in 1081/1082 by John Mauropous, after a vision he had that settled a dispute as to who the greatest of these three hierarchs were, and then went on to compose their service, and this proves the pre-eminent status the Three Hierarchs had among the intellectuals of Constantinople at the time, and they are depicted here together even before the dispute was settled.