"Earth and water" (Greek: γῆ καί ὕδωρ; Persian: آب و زمین) is a phrase that represents the demand by the Achaemenid Empire for formal tribute from surrendered cities and nations.
[1] In Book 5, it is reported that Darius sent heralds demanding earth and water from king Amyntas I of Macedon, which he accepted.
"[6][7] Just before the second Persian invasion of Greece by Xerxes, the Spartans voluntarily sent two men of noble birth to Susa for execution, in atonement for the death of the Darius' heralds.
According to the modern historian J. M. Balcer, the significance of earth and water is that they were Zoroastrian symbols and representative of vassalage to the Persian Empire.
[10] However, according to a new analysis by Daniel Beckman, the ritual of "earth and water" originated from a Neo-Assyrian practice that represented the violent conquest of a city, while in the Achaemenid Empire it symbolized peaceful, voluntary submission.