Council of Hieria
The iconoclast Council of Hieria was a Christian council which viewed itself as ecumenical, but was later rejected by the (still united) Eastern Orthodox and Roman Catholic Churches. It was summoned by the Byzantine Emperor Constantine V in 754 in the palace of Hieria opposite Constantinople. The council supported the iconoclast position of the emperors of this period.
388 bishops attended. No patriarchs or representatives of the five patriarchs were present: Constantinople was vacant while Antioch, Jerusalem and Alexandria were controlled by Saracens.
It styled itself as the Seventh Ecumenical Council, though its opponents described it as the Mock Synod of Constantiople or the Headless Council. Its rulings were overturned almost entirely by the Second Council of Nicaea in 787, which supported the veneration of icons.