Confession against iconoclasm
The second period of Byzantine iconoclasm, during which Peter is placed, saw renewed imperial opposition to the veneration of icons. Peter is remembered for upholding the Orthodox position and suffering for it, which is the basis of his designation as a confessor rather than a martyr.
A concrete witness to Peter's role survives in his correspondence with Saint Theodore the Studite, the abbot of the Studion monastery and a foremost opponent of iconoclasm. Four letters of Theodore the Studite addressed to Peter are known, written between the years 816 and 823, placing Peter within the network of bishops and monastics who resisted the iconoclast measures.