Nethuns governs fresh water, springs and the sea, and Rome received him as Neptune, but the direction of that borrowing is a real scholarly question, and the current of influence may well run from Etruria to Rome rather than the other way, making the Roman sea-god an Etruscan import. Within Etruscan religion Nethuns had a cosmological place as well as a maritime one: in the sixteen-fold division of the sky used by the diviners he was assigned his own region, so that a bolt or a sign from his quarter carried his meaning. His cult mattered in the coastal and lake cities of Etruria, and he is shown as a bearded figure with the trident and sometimes an anchor or sea-creatures.
The unresolved relationship between the names Nethuns and Neptunus, and which people gave the god to which, is a small but telling instance of how entangled early Etruscan and Roman religion really were. More recent scholarship has in fact moved away from treating Nethuns as the clear donor. Several linguists now trace both Nethuns and Neptunus independently to older Italic or Indo-European material, comparing the name to the Celtic river-god Nechtan and the Vedic and Iranian Apam Napat, "grandson of the waters," or deriving it from the Faliscan town-name Nepet (modern Nepi), which would make the sea-god's name originally a local toponym rather than evidence of a direct Etruscan-to-Roman loan in either direction.