Codex Alexandrinus is, but for a few lacunae, one of the three oldest complete texts of the Greek Bible. Dated to the fifth century, its place in the text tradition of the Gospels is unique because it represents the earliest example of a Greek witness to a Byzantine text form. Compared to Codex Sinaiticus and Codex Vaticanus, however, remarkably limited analysis has been performed on Codex Alexandrinus since its acquisition by England in 1627. Indeed, no comprehensive study of the document has been produced in the last century. In recent years there has been growing interest in the devices used to delimit units of text in the biblical manuscripts, as well as the meaning attached to those delimitation decisions. This paper presents an analysis of the unit delimitation used in the Gospels of Codex Alexandrinus in order to shed light on the use of unit markers at the headwaters of the Byzantine text tradition.