Here Augustine relates the tale of the Greek conquest of Egypt by Alexander the Great and its passing on to the control of his generals after his death. Ptolemy, who receive Egypt, ordered the translation of the Hebrew Scriptures into Greek, which gives us the Septuagint. Augustine relates the (certainly mythical) story of its translation by the Scribes, who were confined in cells and yet all managed to produce exactly the same translation. I mention this largely because I'm a fan of Alexander the Great. If you want to become one too, check out Arrian's The Campaigns of Alexander, Robin Lane Fox's Alexander the Great, and Ulrich Wilcken's Alexander the Great (and I recommend reading them in that order).
Some of the church has so far preferred the Septuagint to the original Hebrew (Jerome's Vulgate is a clear exception, as it draws on the Hebrew sources). Augustine believes that we should accept the Septuagint as canon, with the understanding that we may participate in some light textual criticism that adds bits found in the Hebrew but missing from the Septuagint while noting which bits are in the Septuagint but not found in the original Hebrew. The main point of course is that Scripture is not something which comes from men, but rather from God. And we must not take it upon ourselves to judge Scripture and instead ought to be submissive to it--we certainly ought not judge God for the means by which He delivers and preserves it.
[Here of course we say this is one of the few places where Jerome trumps Augustine, which no doubt would have tickled the cranky old scholar pink.]