(1) The Festal Letters of Athanasius with their Index and the Historia Acephala constitute our primary source for chronological details (see below, §2). (2) Along with these come the chronological notices scattered up and down the other writings of Athanasius. These are of course of the utmost importance, but too often lack definiteness. (3) The chronological data in the fifth-century historians, headed by Socrates, are a mass of confusion, and have been a source of confusion ever since, until the discovery of the primary sources, No. (1) mentioned above. They must, therefore, be used only in strict subordination to the latter. (4) More valuable but less abundant secondary notices are to be derived from the Life of Pachomius, from the letter of Ammon (infra, p.487), and from other writers of the day. (5) For the movements of the Emperors the laws in the Codex Theodosianus (ed. Hänel in Corpus Juris Ante-Justiniani) give many dates, but the text is not in a satisfactory condition.
(6) Modern discussions. The conflicting attempts at an Athanasian chronology prior to the discovery of the Festal Letters are tabulated in the Appendix to Newman's Arians, and discussed by him in his introduction to the Historical Tracts (Oxf. Lib. Fathers). The notes to Dr. Bright's article Athanasius in D.C.B., and his introduction to the Hist. Writings of S. Ath., may be profitably consulted, as also may Larsow's Fest-briefe (Leipz., 1852), with useful calendar information by Dr. J. G. Galle, the veteran professor of Astronomy at Breslau, and Sievers on the Hist. Aceph. (Supr. ch. i. §3.)
But by far the most valuable chronological discussions are those of Prof. Gwatkin in his Studies of Arianism. He has been the first to make full use of the best data, and moreover gives very useful lists of the great officials of the Empire and of the movements of the Eastern Emperors. Mr. Gwatkin's results were criticised in the Church Quarterly Review, vol. xvi. pp.392-398, 1883, by an evidently highly-qualified hand . The criticisms of the Reviewer have been most carefully weighed by the present writer, although they quite fail to shake him in his general agreement with Mr. Gwatkin's results.
For the general chronology of the period we may mention Weingarten's Zeit-tafeln (ed.3, 1888) as useful, though not especially so for our purpose, and above all Clinton's Fasti Romani, which, however, were drawn up in the dark ages before the discovery of the Festal Letters, and are therefore antiquated so far as the life of Athanasius is concerned.