Second Council of Lyon

From 7 May to 17 July 1274. It proclaimed union with the Greek Church, promoted by Emperor Michael VIII Palaiologos: the Greek delegates accepted Roman primacy and the Filioque, defined as the Spirit's procession “from the Father and the Son as from one principle.” It issued 31 constitutions, among them Ubi periculum, which regulated the papal conclave. Thomas Aquinas died on his way to the council and Bonaventure died during it.

Convoked by

Pope Gregory X

Canons

31

Catholic Church only (fourteenth ecumenical council in its numbering). The Orthodox Church rejects the union proclaimed there.