The Writing of Time

As far as I can see, the convention that Christ was born on the 25th December dates from the early 3rd Century AD, and is the invention of this neat-minded individual (here's his 1911 Encyclopedia Britannica entry):

AFRICANUS, SEXTUS JULIUS, a Christian traveller and historian of the 3rd century, was probably born in Libya, and may have served under Septimius Severus against the Osrhoenians in A.D. 195. Little is known of his personal history, except that he lived at Emmaus, and that he went on an embassy to the emperor Heliogabalus to ask for the restoration of the town, which had fallen into ruins. His mission succeeded, and Emmaus was henceforward known as Nicopolis. Dionysius bar-Salibi makes him a bishop, but probably he was not even a presbyter. He wrote a history of the world (Chronografiai, in five books) from the creation to the year A.D. 221, a period, according to his computation, of 5723 years. He calculated the period between the creation and the birth of Christ as 5499 years, and ante-dated the latter event by three years. This method of reckoning became known as the Alexandrian era, and was adopted by almost all the eastern churches. The history, which had an apologetic aim, is no longer extant, but copious extracts from it are to be found in the Chronicon of Eusebius, who used it extensively in compiling the early episcopal lists. There are also fragments in Syncellus, Cedrenus and the Paschale Chronicon. Eusebius (Hist. Ecc. i. 7, cf. vi. 31) gives some extracts from his letter to one Aristides, reconciling the apparent discrepancy between Matthew and Luke in the genealogy of Christ by a reference to the Jewish law, which compelled a man to marry the widow of his deceased brother, if the latter died without issue. His terse and pertinent letter to Origen, impugning the authority of the apocryphal book of Susanna, and Origen's wordy and uncritical answer, are both extant. The ascription to Africanus of an encyclopaedic work entitled Kestoi (embroidered girdles), treating of agriculture, natural history, military science, &c., has been needlessly disputed on account of its secular and often credulous character. Neander suggests that it was written by Africanus before he had devoted himself to religious subjects. For a new fragment of this work see Oxyrhynchus Papyri (Grenfell and Hunt), iii. 36 ff.

This now-lost Chronographiae, 'Writings on Time' interests me very much. As Hagith Sivan notes, 'Africanus' chronological system, underpinned by the Judaeo-Christian conviction that the duration of history as a whole amounted to 6000 years, in accordance with the six days of creation. This straitjacket forced Africanus to be both ingenuous and imaginative in devising a system that ... was, on the whole, internally coherent.' (Alden Mosshammer 'determines that Africanus dated the Incarnation to the 25th of March in the year 5501 from Adam (= 1 B.C.), and the Resurrection to March 25th, Olympiad 202.2, year 5532 from Adam (= A.D. 31)') This will to neatness is the most fascinating thing of all: for why should time be neat? That other great innovator in the chronographic arts, H G Wells, didn't think it did.