>John Koch ("Ériu, Alba, and Letha", Emania 9, 1991) agrees, although
>he calls "Latium" a "pedantic transfer". He claims that these names,
>which include Old Breton "Letau" and Romano-Celtic "Letavia", are
>cognate with Vedic PRthivî 'The Divinised Earth' -- ultimately from
>an IE word meaning "the broad one". He suggests that Celtic as well
>as Indic employed this as a feminine theonym, citing the dedicatory
>inscription MARTI CICOLLUI ET LITAVI from Southern Gaul. "The Gaulish
>cult of Litavi(s) shows that the name had once designated the divinised
>land for Continental Celts and that the Brittonic and Irish have merely
>preserved a usage anciently current in Gaul itself. The inscriptional
>evidence from the far south of Gaul [Narbonne] indicates that the name
>had once covered a region far larger than Brittany."
Makes sense to me.
Litaui(a) and Prithvi both come from PIE *pel@-tu- a suffixed form of
*pel@- "Flat/to spread" (the Celtic and Indioc forms thus = *Plt-u-ieH2).
This root is also behind the Germanic *felthuz, giving English field.
Litavi(a) and Prthvi, then, represent "The (Great) Field," a suitable
epithet for the Earth.
Litaui(a) in Gaul is connected on a few inscriptions to Mars Cicollus
(perhaps cico- is the same as Irish cich "flesh" ?). In another inscription,
Mars Cicollus is connected with Bellona ("War Goddess"), perhaps indicating
that Bellona is an alternate name for Litaui(a). I think the fact that Letha
and Llydaw became the names for North Western Gaul in Irish and Welsh,
replacing Armorica, strengthens the notion that Britain and Ireland had
strong connections to Gaulish populations - especially if Litaui(a) is some
type of Gaulish Earth Goddess.