Most of the earliest surviving Uncial manuscripts were written in Northern Africa. The oldest datable Uncial manuscript is a copy of Augustinus, Libri II ad Interrogata Simpliciani, etc. (St. Petersburg, Public Library Ms. Q. V. 1, 3), written between 396 and 426 CE probably in Hippo Regius , the ancient name for the city of Annaba, Algeria. This was described by E. A. Lowe, in Codices Latini Antiquiores XI (1966) no. 1613, and the Supplement to C.L.A. (1971) p. ix, and plate 3A. Lowe wrote:
"Written probably in Africa, to judge by the script of one of the two hands though the other is manifestly trained in the Italian manner. African origin is supported by W. M. Green's brilliant hypothesis that the volume was produced at Hippo in the author's early episcopacy. This renders it one of the most precious in the entire C.L.A. series. The manuscript belonged to Corbie where it is mentioned in several catalogues. Came to Saint Germain-des-Prés in 1638, where it bore the number 254. Acquired by Peter Dubrowsky [Dubrovsky] in 1791 and by the Imperial Library in 1805."
"It has been suggested that the Uncial script was deliverately devised, at the time when Constantine was Emperor (AD 306-337), as a specifically Christian bookhand to replace the Square and Rustic capitals used for 'pagan' classics. However, there are some ancient scripts and inscriptions with certain Uncial characteristics, which clearly pre-date the time of Constantine. The Timgad inscription of the 2nd or 3rd century, also has letters which are very similar to Uncial forms (see Stanley Morison, Politics and Script, page 63).
"Furthermore, the existence of some early Christian texts written in Rustics, like the fragment of the Gospel of John (Aberdeen, University Library, Papyrus 2a) and the Epistle to the Ephesians (Florence, Ms. Laur. P./S. 1, 1306), as well as at least one 'pagan' author, Cicero, written in the 4th century in Uncials (Vatican, Ms. Lat. 5757), cast doubt on this common assertion" (Stan Knight, Historical Scripts fron Classical Times to the Renaissance  B6 (p. 33)