 The earliest, and therefore probably most reliable, account is that of the medical writer Thessalos, who in the 5th century BC wrote that the attackers discovered a secret water pipe leading into the city after it was broken by a horse's hoof.An "asclepiad" named Nebros, or, according to another version the Athenian Solon advised the allies to poison the water with hellebore.The hellebore soon rendered the defenders so weak with diarrhea that they were unable to continue resisting the assault.