an Italian prelate, was born at Corneto (Tuscany), in the latter part of the l1th century. Although of obscure parentage, he attained to the first dignities of the Church. Having been sent to England by Innocent VIII, he gained by that mission the favor of Henry VII, who in 1503 appointed him bishop of Hereford, and in the year following transferred him to the see of Bath and Wells. Meanwhile pope Alexander VI made him his secretary and gave him the cardinal's hat. It is said that this pontiff, in trying to poison him, poisoned himself. Castellesi was exiled by Julius II, and called back again by Leo X; but he entered into a conspiracy against the latter pope, and was condemned to pay a certain sum; he then fled from Rome, but it has never been ascertained precisely what became of him. He left, De Vera Philosophia (Bologna, 1507): — De Sermone Latino (Basle, 1513): — De Narratione, et Julii III, Liter (Venice, 1534). See Hoefer, Nouv. Biog. Gé neralé, s.v.