Sextus Julius Africanus (c. 160 – c. 240) was a Christian traveler and historian of the late second and early third centuries. He is important chiefly because of his influence on Eusebius, on all the later writers of Church history among the Church Fathers, and on the whole Greek school of chroniclers.
The Suidas claims Africanus was a "Libyan philosopher", while Gelzer considers him of Roman descent. Julius called himself a native of Jerusalem – which some scholars consider his birthplace – and lived at the neighbouring Emmaus. His chronicle indicates his familiarity with the topography of historic Judea.
Little of Africanus's life is known and all dates are uncertain. One tradition places him under the Emperor Gordianus III (238–244), others mentions him under Severus Alexander (222–235). He appears to have known Abgar VIII.(176–213).
Africanus may have served under Septimius Severus against the Osrhoenians in 195. He went on an embassy to the emperor Severus Alexander to ask for the restoration of Emmaus, which had fallen into ruins. His mission succeeded, and Emmaus was henceforward known as Nicopolis.
Africanus traveled to Greece and Rome and went to Alexandria to study, attracted by the fame of its catechetical school, possibly about the year 215. He knew Greek (in which language he wrote), Latin, and Hebrew. He was at one time a soldier and had been a pagan; he wrote all his works as a Christian.
Whether Africanus was a layman or a cleric remains controversial. Louis-Sébastien Le Nain de Tillemont argued from Africanus's addressing the priest Origen as "dear brother" that Julius must have been a priest himself but Gelzer points out that such an argument is inconclusive.
Africanus wrote Chronographiai, a history of the world in five volumes. The work covers the period from Creation to the year AD 221. He calculated the period between Creation and Jesus as 5500 years, placing the Incarnation on the first day of AM 5501 (our modern March 25 1 BC). (Note that this dating implies that the birth of Jesus was in December, nine months later.) This method of reckoning led to several Creation eras being used in the Greek Eastern Mediterranean, which all placed Creation within one decade of 5500 BC.
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 George Syncellus, Cedrenus and the Chronicon Paschale. Eusebius 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 of Levirate marriage, 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 part of the Book of Daniel that tells the story of Susanna, and Origen's wordy and uncritical answer, are both extant.
The ascription to Africanus of an encyclopaedic work entitled Kestoi (Κέστοι "Embroidered"), treating of agriculture, natural history, military science, etc., has been disputed on account of its secular and often credulous character. August Neander suggested that it was written by Africanus before he had devoted himself to religious subjects. A fragment of the Kestoi was found in the Oxyrhynchus papyri. According to the New Schaff-Herzog Encyclopedia of Religious Knowledge, the Kestoi "appears to have been intended as a sort of encyclopedia of the material sciences with the cognate mathematical and technical branches, but to have contained a large proportion of merely curious, trifling, or miraculous matters, on which account the authorship of Julius has been questioned. Among the parts published are sections on agriculture, liturgiology, tactics, and medicine (including veterinary practise)."
Only fragments of his religious writings have been preserved. One fragment deals with eschatology.
After referring to the standard interpretation of the 'ram' and the 'he-goat', as symbolizing Persia and Greece, Africanus suggested that the 2300 days might be taken form months, totaling about 185 years which he applied to the time from the Capture of Jerusalem to the 20 year of Artaxerxes. He seems to be the only one who developed this interpretation.
Africanus begins the seventy weeks Daniel 9 with the twentieth year of Artaxerxes, in Olympiad 83, year 4, (444 B.C.) and ends the period in Olympiad 202, year 2, (31 A.D.) or 475 solar years inclusive, which would be equivalent to 490 uncorrected lunar years. 
This work does not survive except in fragments, chiefly those preserved by Eusebius and Georgius Syncellus. In turn Africanus preserves fragments of the work of Polemon of Athens' Greek History.
Polemon, &c.] He seems to have lived in the Time of Ptolemy Epiphanes; concerning which, see that very useful Book of the famous Gerrard Vossius, of the Greek Historians. Africanus says, the Greek Histories were wrote by him; which is the same Book Athenæus calls, ???. His Words are these: "In the Reign of Apis, king of Argos the Son of Phoroneus, Part of the Egyptian Army went out of Egypt, and dwelt in Syria called Palestine, not far from Arabia. As Africanus preserved the Place of Polemon, so Eusebius in his Chronology preserved that of Africanus. (p. 64 at Google Books)