10 But at this synod of Ephesus, which St. Leo rightly called a 'Robbers' council', Dioscorus and Eutyches carried off everything with a high hand. The first places in the council were denied to the apostolic delegates; the letters of the pope were not allowed to be read, the votes of the bishops were extorted by threats and stratagems; among others Flavian was accused of heresy, deprived of his pastoral ministry and thrown into prison, where he died. The rash fury of Dioscorus even went to the length of criminally hurling an excommunication at the Apostolic See itself. As soon as St. Leo learnt from the deacon Hilary of the evil deeds of this council, he condemned and annulled all the decrees and decisions made by it. His grief at these crimes was greatly increased by the frequent appeals to his authority made by the numerous bishops who had been deposed.
Source: Sempiternus Rex Christus (Vatican.va)