Palladium (mythology)
In Greek and Roman mythology, a palladium or palladion was an image of great antiquity on which the safety of a city was said to depend. "Palladium" especially signified the wooden statue (xoanon) of Pallas Athena that Odysseus and Diomedes stole from the citadel of Troy and which was later taken to the future site of Rome by Aeneas. The Roman story is related in Virgil's Aeneid and other works.
In English, since circa 1600, the word "palladium" has meant anything believed to provide protection or safety — a safeguard.
Read more about Palladium (mythology): The Athenian Palladium, Palladium-equivalents in Other Cultures