First Council of Constantinople
First Council of Constantinople, Canon III
Creed and received canons; later attributions identified in the text; not the full proceedings
Canon III
The Bishop of Constantinople, however, shall have the prerogative of honour after the Bishop of Rome; because Constantinople is New Rome.
Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.
Source: First Council of Constantinople (CCEL)