Cyril Bailey, The Religion of Ancient Rome
“ Theology.—The characteristic appellation of a divine spirit in the oldest stratum of the Roman religion is not deus, a god, but rather numen, a power: he becomes deus when he obtains a name, and so is on the way to acquiring a definite personality, but in origin he is simply the 'spirit' of the 'animistic' period, and retains something of the spirit's characteristics. ”
