Bulis and Sperthias were two Spartan noble youths who volunteered to sacrifice their lives in order to give restitution for the lives of two Persian ambassadors who had been put to death by the Spartans. Several years previously, the ambassadors had approached the city to ask for soil and water as a sign of submission to the Great King of Persia, and were promptly tossed into a well. To make amends for this breach of diplomatic etiquette, the two set out on a journey across Greece and Asia Minor on their way to Susa, the Persian capital. On their way they were hosted and entertained by Persians as well as Greeks who were aware of their mission. Most notable was a meeting with Hydarnes, the Satrap of Asia Minor, who attempted to talk them into allying themselves with Xerxes. Their reply was as follows: "Thou knowest indeed what it is to be a slave, but of freedom thou hast never made trial, whether it be sweet or no. Surely if thou hadst made such trial thou wouldst counsel us to fight for it, not with the spear only, but also with the battle-ax."
Upon their arrival in Susa, they refused to bow before the Great King, but presented themselves as willing to offer their lives to make atonement for the murdered ambassadors. Xerxes replied as follows, before sending them back to Sparta, unharmed: "The Spartans, when they do such things overthrow all law and justice among men; but I will not make myself like unto them. I will neither do the thing for the doing of which I reproach them, nor will I loose them from their guilt by slaying the men that they have sent to me."