Galen, Commentary on Hippocrates’ Epidemics (3.2):
“Here is a small example of what Ptolemy Euergetes did to the Athenians, showing how eager he was for the acquisition of ancient books. He gave them a security of fifteen talents of silver in exchange for borrowing the official copies of Sophocles, Euripides, and Aeschylus for the sake of making copies of them and returning them intact to the Athenians. He had copies worked up in exceedingly fine fashion on the most beautiful papyrus, and then kept the copies which the Athenians had sent him, while sending to them the finely-wrought copies and saying that they could keep the fifteen talents and take the new copies in exchange for the old ones. Even if Ptolemy had not sent them the new books, the Athenians could do nothing since they had taken the silver on the understanding that they could keep it if Ptolemy did not return the books. And so, they took the new copies and held on to the silver.”
ὅτι δ’ οὕτωϲ ἐϲπούδαζε περὶ τὴν <ἁπάντων> τῶν παλαιῶν βιβλίων κτῆϲιν ὁ Πτολεμαῖοϲ ἐκεῖνοϲ, οὐ μικρὸν εἶναι μαρτύριόν φαϲιν ὃ πρὸϲ ᾿Αθηναίουϲ ἔπραξεν. δοὺϲ γὰρ αὐτοῖϲ ἐνέχυρα πεντεκαίδεκα τάλαντ’ ἀργυρίου καὶ λαβὼν τὰ Σοφοκλέουϲ καὶ Εὐριπίδου καὶ Αἰϲχύλου βιβλία χάριν τοῦ γράψαι μόνον ἐξ αὐτῶν, εἶτ’ εὐθέωϲ ἀποδοῦναι ϲῶα, καταϲκευάϲαϲ πολυτελῶϲ ἐν χάρταιϲ καλλίϲτοιϲ, ἃ μὲν ἔλαβε παρ’ ᾿Αθηναίων κατέϲχεν, ἃ δ’ αὐτὸϲ κατεϲκεύαϲεν ἔπεμψεν αὐτοῖϲ παρακαλῶν <κατα>ϲχεῖν τε τὰ πεντεκαίδεκα τάλαντα καὶ λαβεῖν ἀνθ’ ὧν ἔδοϲαν βιβλίων παλαιῶν τὰ καινά. τοῖϲ μὲν οὖν ᾿Αθηναίοιϲ, εἰ καὶ μὴ καινὰϲ ἐπεπόμφει βίβλουϲ, ἀλλὰ κατεϲχήκει τὰϲ παλαιάϲ, οὐδὲν ἐνῆν ἄλλο ποιεῖν, εἰληφόϲι γε τὸ ἀργύριον ἐπὶ ϲυνθήκαιϲ τοιαύταιϲ, ὡϲ αὐτοὺϲ <αὐτὸ> καταϲχεῖν, εἰ κἀκεῖνοϲ κατάϲχοι τὰ βιβλία, καὶ διὰ τοῦτ’ ἔλαβόν τε τὰ καινὰ καὶ κατέϲχον καὶ τὸ | ἀργύριον.