Various measures had been taken against the heresy of the Adoptionists, both by Karl and by the Pope, Adrian. In course of time Karl sent the treatise of Felix to Alcuin, who was at the time in England, and Alcuin returned to France, never again to visit his native country. Simeon of Durham tells us that the English bishops made him their representative for the refutation of Felix. As such, probably, in part, but also by the special wish of Karl, he attended the Council of Frankfort in 794, and though only a deacon, argued against Felix. Felix was condemned. Alcuin’s argument was at Karl’s request or command developed into a treatise in seven books; and he wrote also a treatise in three books against Elipandus. We have these ten books. They fill 220 very closely printed columns in Migne’s series. The books against Felix are among the best and most independent of Alcuin’s dogmatic work. This by no means ended the matter. In the year 798 Karl sent to Alcuin a treatise by Felix, which he desired Alcuin to refute. Alcuin’s reply has been the subject of so much controversy that it will be well to give it as literally as possible. The point is, the place assigned to the Pope as a judge of doctrine. I only quote that part of the very long letter. [Sidenote: Ep. 100. July, 798.] “I beseech you, if it please your piety, that a copy of the treatise be sent to the apostolic lord [that is of course the Pope] and another to Paulinus the patriarch [of Aquileia]; similarly to Richbon [of Trèves] and Theodulf [of Orleans] bishops, doctors, and ministers; that they may (_singuli_) severally answer for themselves.[168] Your Flaccus [Alcuin] labours with you in giving account of the catholic faith. Allow him sufficient time to consider with his pupils, quietly and carefully, the opinions of the Fathers, what each has said on such views as this subverter has set forth in his book. Then, at a time appointed by you, let the answers of the above several persons (_singulorum_) be brought to you. And whatever of opinion or of meaning in that book is found to be contrary to the catholic faith, let it be overthrown by catholic quotations. And if the writings of all [of the above] sound forth equally and concordantly in profession or defence of the catholic faith, it will be clear that one spirit speaks through the voice and heart of all; but if anything diverse is found in the words or the writings (_dictis vel scriptis_) of any one of them, let it be judged which is most in accord with sacred scripture and the catholic fathers, and give the palm to him who is most firm in the divine evidences.”