To Valerianus, Bishop of Illyricum. Or, in some mss., the Illyrians.  Valerianus, bishop of Aquileia, was present at the Synod held in Rome in 371 (Theodoret, Hist. Ecc. ii. 2.) and also at the Synod in the same city in 382.  (Theod. Ecc. Hist. v. 9, where see note.)  Dorotheus or Sabinus had brought letters from Athanasius and at the same time a letter from Valerianus.  Basil takes the opportunity to reply.