Basil of Caesarea, also called Saint Basil the Great, (329 or 330[5] – January 1, 379) (Greek: Ἅγιος Βασίλειος ὁ Μέγας) was the Greek bishop of Caesarea Mazaca in Cappadocia, Asia Minor (modern-day Turkey). He was an influential theologian who supported the Nicene Creed and opposed the heresies of the early Christian church, fighting against both Arianism and the followers of Apollinaris of Laodicea. His ability to balance his theological convictions with his political connections made Basil a powerful advocate for the Nicene position.

Of Saint Basil the extant letters, according to popular ascription, number three hundred and sixty-six. Of these three hundred and twenty-five, or, according to some, only three hundred and nineteen are genuine. They are published in three chronological divisions, the 1st, (Letters 1–46) comprising those written by Basil before his elevation to the episcopate; the second (47–291) the Letters of the Episcopate; the third (292–366) those which have no note of time, together with some that are of doubtful genuineness, and a few certainly spurious.1736 They may be classified as (a) historical, (b) dogmatic, (c) moral and ascetic, (d) disciplinary, (e) consolatory, (f) commendatory, and (g) familiar. In the historic we have a vivid picture of his age. The doctrinal are of special value as expressing and defending the Nicene theology. The moral and ascetic indicate the growing importance of the monastic institution which Athanasius at about the same time was instrumental in recommending to the Latin Church. The disciplinary, (notably 188, 199, and 217), to Amphilochius, illustrate the earlier phases of ecclesiastical law. The consolatory, commendatory, and familiar, have an immediate biographical value as indicating the character and faith of the writer, and may not be without use alike as models of Christian feeling and good breeding, and as bringing comfort in trouble to readers remote in time and place. The text in the following translation is that of Migne’s edition, except where it is stated to the contrary. Of the inadequacy of the notes to illustrate the letters as they deserve no one can be more vividly conscious than myself. But the letters tell their own story.
Cf. http://www.ccel.org/ccel/schaff/npnf208.ix.i.html