The ancilia were twelve figure-of-eight bronze shields central to the Roman cult of Mars. Tradition held that one shield fell from the sky during the reign of the second king, Numa Pompilius, as a token of Rome's destiny, and that eleven copies were made so that the true shield could not be singled out and stolen. They ranked among the pledges of empire and were kept in the Temple of Mars, brought out for the festivals of March.
Roman legend, recorded by Livy and Plutarch, holds that under the second king, Numa Pompilius, a single bronze figure-of-eight shield fell from the sky as a pledge of Rome's destiny. To protect it from theft, Numa commissioned the smith Mamurius Veturius to forge eleven identical copies, so that no thief could ever be certain which of the twelve was the true, heaven-sent shield. The word ancile itself, and the derived English adjective describing something as an inviolable safeguard, entered later European heraldic and antiquarian vocabulary as a classical allusion, though the specific bronze figure-of-eight shield shape attested in Roman art for the Ancilia has no surviving physical example securely identified as one of the twelve, since, as with the Palladium, the entire tradition rests on Roman literary description rather than on any archaeological find that can be matched to it with confidence.