Aeneas Tacticus, Fragments LI: on the Sending of Messages”
“People who plan to work with traitors need to know how to send messages. Send them like this. Have a man be sent openly carrying some note about other matters. Have a different letter be secretly placed under the sole of the sandals of the person carrying the first message. Sew it between the layers and have it inscribed on tin to be safeguarded against mud and water.
Once the messenger has arrived to his destination and he has rested for the night, let the intended recipient remove the stitches from the sandals, take the message out, write a response secretly, and send the messenger back once he has written some public message to carry openly. In this way, not even the messenger will know what he carries.”
Τοῖς κεχρημένοις προδόταις ἀναγκαῖον εἰδέναι πῶς ἐπιστολὰς δεῖ αὐτοὺς εἰσπέμπειν. ἀπόστελλε γοῦν οὕτως. πεμπέσθω ἀνὴρ ἐν τῷ φανερῷ φέρων1 ἐπιστολήν τινα περὶ ἄλλων πραγμάτων. τοῦ δὲ πορεύεσθαι μέλλοντος κρυφαίως αὐτοῦ εἰς τὸ τῶν ὑποδημάτων πέλμα ἐντεθήτω εἰς τὸ μεταξὺ βιβλίον καὶ καταραπτέσθω· πρὸς δὲ τοὺς πηλοὺς καὶ τὰ ὕδατα εἰς κασσίτερον ἐληλασμένον2 γραφέσθω πρὸς τὸ μὴ ἀφανίζεσθαι ὑπὸ τῶν ὑδάτων τὰ γράμματα. ἀφικομένου δὲ πρὸς ὃν δεῖ3 καὶ ἀναπαυομένου νυκτὸς ἀναλυέτω τὰς ῥαφὰς τῶν ὑποδημάτων καὶ ἐξελὼν ἀναγνούς τε καὶ4 ἄλλα γράψας λάθρᾳ ἀποστελλέτω τὸν ἄνδρα, ἀνταποστείλας καὶ δούς τι5 φέρειν φανερῶς· οὕτως γὰρ οὔτε ἄλλος οὔτε ὁ φέρων εἰδήσει.