 Leo IX sent a letter to Michael I in 1054, citing a large portion of the Donation of Constantine, believing it genuine.Leo assured Michael that the donation was completely genuine, not a fable, so only the apostolic successor to Peter possessed that primacy and was the rightful head of all the Church.Before his death, Leo IX had sent a legatine mission under Cardinal Humbert of Silva Candida to Constantinople to negotiate with Patriarch Michael Cerularius in response to his actions concerning the church in Constantinople.