Eusebius, in Vit. Constant. 1. ii. c. 64-72. The principles of toleration and religious indifferrence contained in this epistle have given great Offence to Baronius, Tillemont, etc., who suppose that the emperor had some evil counsellor, either Satan or Eusebius, at his elbow. See Jortinss Remarks, tom. ii. p. 183.