Scribonius Largus was a physician in the time of Claudius. He was the author of a collection of medical recipes, written in 47-48 A.D.
The work begins with a preface; then there is an index; and then the recipes.
At the end of the preface, Largus writes:
Primum ergo ad quae vitia compositiones exquisitae et aptae sint, subiecimus et numeris notavimus, quo facilius quod quaeretur inveniatur. Deinde medicamentorum, quibus compositiones constant, nomina et pondera vitiis subiunximus.
So firstly, the illnesses for which medicines are sought-for and found, we have subjoined and numbered, so that the seeker may find more easily. Then we have subjoined the names and amounts of the medicaments which the medicines for illnesses consist of.
The second list has not been preserved, but these words are followed in the edition by a list of illnesses, and for each a numeral.
What this demonstrates is that the concept of producing a numbered table of contents did exist in the time of Claudius, and, therefore, probably earlier.