A possible translation

Paleo-

Pa´le`o-
1. A combining form meaning old, ancient; as, palearctic, paleontology, paleothere, paleography

VARIANT FORMS: or pale– or palaeo– or palae–
PREFIX: 1. Ancient; prehistoric; old: paleobotany. 2. Early; primitive: Paleozoic.
ETYMOLOGY: Greek palaio-, from palaios, ancient, from palai, long ago. See kwel-2 in Appendix I.

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... rich history. From the Paleo-Venetian to the Gaelic period, testified
by some land toponyms such as Canzago and Tiago. • Ospitale ..

This is related to the pre-Roman period:
"The colonization process covered the whole of Veneto, city after city, and meant also the building of long important roads. Both actions, by inserting the Roman culture into the territory, aimed at consolidating the conquest of the area and allowed for the diffusion of the Roman civilization into the *Paleo-veneto* world. The roads had not just military and commercial uses but were also roads for the transmission of culture. During the years 150-70 B.C. important roads were built, such as the Postumia (Genoa - Aquileia), the Aurelia (Padua - Asolo) and the Annia (Adria - Aquileia)
http://people.clemson.edu/~bentonc/5769.html

I would avoid "-venetian" since this has to do with (post-Roman)Venice
:)