Lua was an obscure but highly archaic Italic goddess, named in old religious texts as the consort of Saturn — Lua Mater, or Lua Saturni — and she was the recipient of a strange and terrible offering: the arms of defeated enemies. After a victory, the Roman general would heap up the captured weapons on the field of battle, sacrifice them by fire, and dedicate them to Lua. In this destruction the spoils were not enriching the victor but were being given over to a divinity who consumed them; the rite was called the dedicatio, and was distinguished from the spoils that were taken back to Rome and dedicated to Jupiter Feretrius or carried in triumph.

The name Lua was understood by the Romans to derive from the verb luere, "to release, to wash away, to expiate"; the goddess was the power that purified the battlefield by destroying its weapons, that the victor might not be polluted by carrying home all that he had captured. So at least some pious survival from victory had to be given to her — and among the most pious of generals, like Aemilius Paullus and Marius and Scipio Africanus, this was conscientiously done.

By the imperial period Lua was little remembered; her name is preserved chiefly in the antiquarian compilations of Varro and Festus and in occasional inscriptions. The classical mythographers found her hard to place, and she has no Greek equivalent. She is one of those archaic Italic powers — alongside Vacuna, Furrina, Robigus, and the rest — whose original significance was lost even to the Romans of Cicero's day, but whose names continued to be uttered at the proper points in the priestly calendar.