Palladium

a celebrated image of Pallas Athene. It was said to have fallen from heaven into the city of Troy, and the safety of the city was supposed to depend on the preservation of this image. During the siege of Troy, Ulysses and Diomed entered the city in disguise and stole the palladium, carrying it off to the Greek camp. The word palladium was applied also to any image of Pallas. The term palladium has passed into proverbial use and especially in the expression the "palladium of liberty."