The 1897 publication of the Oxyrhynchus papyri contains an interesting fragment, P.Oxy. 10. This is third century A.D., and is in the Bodleian. It contains parts of two consecutive columns from the lost Πεντέμυχος of Pherecydes of Syros. The author wrote in the 6th century BC and was one of the first Greek prose writers. A chunk of this work is preserved in Clement of Alexandria, Stromateis 6, and most of this chunk is contained, without variation, in the first column of the papyrus. The content of the fragment seems to be a speech by Zeus from the marriage of Zeus and Hera. The work was extant at this time in full, as Diogenes Laertius tells us (Vit. Phil. i. 11. 6), and indeed he quotes its opening words.
The interest of this papyrus for us, however, is the presence of a numeral in the margin.
On this the editor comments: “The numeral in the margin probably denotes a new chapter, and indicates that this was a continuous work, not a collection of extracts.”
If so, this would be interesting as showing how a chapter was marked in an ancient prose work in the 3rd century AD.