At Millesgården, the sculptor Carl Milles’s studio and museum on the island of Lidingö outside Stockholm, a copy of the Capitoline Wolf stands in the open air, green with patina, the two infants nursing beneath the she-wolf’s belly on a red granite plinth. Ivy climbs the wall behind it. A stone face — a garden ornament — watches from the wall above. The composition is so familiar as to have become almost invisible through repetition: the wolf alert, ears pricked, facing left with a wariness that has not relaxed in two thousand years of bronze casting; the twins below, pudgy and insistent, entirely unconcerned with the predator feeding them. The image is Rome’s founding symbol, its most exported icon, the picture that appeared on Roman coins in the second century BC and on Italian government documents in the twenty-first century AD. It has been in continuous circulation as a symbol of Roman identity for over two millennia, which is not an achievement many images can claim.

Rome was not original in its theology, and it did not pretend to be. The Romans were systematic borrowers of divine power, operating on the practical assumption that a god who worked was worth incorporating regardless of origin. The result was a pantheon that was Greek at its core, overlaid with indigenous Italian tradition, supplemented by imports from Egypt, Persia, and Syria, and eventually contested and replaced by a monotheism that originated in Judea. Roman religion was an accumulation, not a creation.