Herodian, History 4.8:
“Caracalla came to Ilium, and as he visited all of the ruins of the city, he came to the tomb of Achilles. Decorating it lavishly with garlands and flowers, he imitated Achilles again. Seeking a Patroclus, he did something like this. He had a particularly beloved freedman named Festus who was the chief imperial secretary. This man Festus died while Caracalla was in Ilium, and some say that he was taken off by poison so that he could have a funeral like Patroclus, but others say that he simply died of an illness.”
ἧκεν ἐς ῎Ιλιον. ἐπελθὼν δὲ πάντα τὰ τῆς πόλεως λείψανα, ἧκεν ἐπὶ τὸν ᾿Αχιλλέως τάφον, στεφάνοις τε κοσμήσας καὶ ἄνθεσι πολυτελῶς πάλιν ᾿Αχιλλέα ἐμιμεῖτο. ζητῶν δὲ καὶ Πάτροκλόν τινα ἐποίησέ τι τοιοῦτον. ἦν αὐτῷ τις τῶν ἀπελευθέρων φίλτατος, Φῆστος μὲν ὄνομα, τῆς δὲ βασιλείου μνήμης προεστώς. οὗτος ὄντος αὐτοῦ ἐν ᾿Ιλίῳ ἐτελεύτησεν, ὡς μέν τινες ἔλεγον, φαρμάκῳ ἀναιρεθεὶς ἵν’ ὡς Πάτροκλος ταφῇ, ὡς δ’ ἕτεροι ἔφασκον, νόσῳ διαφθαρείς.