[Can't we banish him forever? From the entire country?] Soon after the battle of Marathon in 490 B., the Athenians began the practice of ostracism, a form of election designed to curb the power of rising tyrants
The water in each tank was taken from the same body of water at the same time. The only difference is that one tank also contains oysters. A single adult oyster can filter and clean up to 50 gallons of water every day!