In 431 BCE, while besieging Athens, Nabis received a letter from a polemarch instructing him to interrogate a spy of Kleon's who was caught trying to sneak through and bought a ship for Mytilene. He later had the spy held in a cage in the Mt. Pentelikos Marble Quarry north of the Sieged Plains.
Shortly afterwards, Nabis and his men were eliminated by the misthios Kassandra, whom Kleon had hired to free Athens from the siege. In doing so, Nabis' letter was recovered by Kassandra, who brought it to Kleon.