THE ORIGINS OF ABC - a wide-ranging history of the alphabet in a post at John Boardley's I Love Typography blog. I've skimmed it over quickly and the parts about which I know something look pretty accurate.
Nitpick: the latest surviving cuneiform text dates itself to 74-75 CE, not the fifth century CE. Aspects of Mesopotamian religion did continue into late antiquity (e.g., the Nabu cult in Barsippa), so that may be what the author was thinking about.
But looks like a good and useful popular synthesis overall.
Via various people on Facebook.