16 Not content with this, St. Leo, having made perfectly clear "what the Catholic Church universally believes and teaches concerning the mystery of the Lord's incarnation,'' (11) followed up this Epistle to Flavian with a condemnation of the Ephesine Council of 449. At this council the supporters of Eutyches had, by violent and unconstitutional means, done all they could to impose the groundless dogmatic assertions of this "very foolish and exceedingly ignorant man,'' (12) who obstinately maintained that there was only one nature in Christ, the divine nature.
Source: Aeterna Dei Sapientia (Vatican.va)