1. De Fide. The chief of these are the Five Books on the Faith, of which the two first were written in compliance with a request of the Emperor Gratian, a.d. 378. Books III.–V. were written in 379 or 380, and seem to have been worked up from addresses delivered to the people [V. prol. 9, 11; III. 143; IV. 119]. This treatise vindicates the Divinity of Christ from the attacks of the Arians, and has always enjoyed the highest reputation, being quoted and referred to again and again.