Porphyry, Life of Plotinus 24
“This is, therefore, our story of Plotinus’ life. When he assigned to me the arrangement and editing of his publications, I promised him when he was still alive and I also guaranteed our other friends to do that. So, first, I did not think it just to allow his books to be out of order from the time they were published but have imitated Apollodoros the Athenian and the peripatetic Andronicus. They first gathered the works of Epikharmos the comedic poet into ten collections and the second ordered the works of Aristotle and Theophrastos by subject matter, collecting into the same place similar theoretical discussions.
In a similar way, in fact, since I had 54 works of Plotinus, I separated the books into six groups of nine volumes each, chancing upon the final number six along with nines quite happily. Once I assembled similar topics into each Ennead, I gave the first place to the more tractable problems.”
Τοιοῦτος μὲν οὖν ὁ Πλωτίνου ἡμῖν ἱστόρηται βίος. Ἐπεὶ δὲ αὐτὸς τὴν διάταξιν καὶ τὴν διόρθωσιν τῶν βιβλίων ποιεῖσθαι ἡμῖν ἐπέτρεψεν, ἐγὼ δὲ κἀκείνῳ ζῶντι ὑπεσχόμην καὶ τοῖς ἄλλοις ἑταίροις ἐπηγγειλάμην ποιῆσαι τοῦτο, πρῶτον μὲν τὰ βιβλία οὐ κατὰ χρόνους ἐᾶσαι φύρδην ἐκδεδομένα ἐδικαίωσα, μιμησάμενος δ᾿ Ἀπολλόδωρον τὸν Ἀθηναῖον καὶ Ἀνδρόνικον τὸν Περιπατητικόν, ὧν ὁ μὲν Ἐπίχαρμον τὸν κωμῳδιογράφον εἰς δέκα τόμους φέρων συνήγαγεν, ὁ δὲ τὰ Ἀριστοτέλους καὶ Θεοφράστου εἰς πραγματείας διεῖλε τὰς οἰκείας ὑποθέσεις εἰς ταὐτὸν συναγαγών· οὕτω δὴ καὶ ἐγὼ νδ ὄντα ἔχων τὰ τοῦ Πλωτίνου βιβλία διεῖλον μὲν εἰς ἓξ ἐννεάδας τῇ τελειότητι τοῦ ἓξ ἀριθμοῦ καὶ ταῖς ἐννεάσιν ἀσμένως ἐπιτυχών, ἑκάστῃ δὲ ἐννεάδι τὰ οἰκεῖα φέρων συνεφόρησα δοὺς καὶ τάξιν πρώτην τοῖς ἐλαφροτέροις προβλήμασιν. Ἡ μὲν γὰρ πρώτη ἐννεὰς ἔχει τὰ ἠθικώτερα τάδε·