The entire area was under Austrian rule in 1863; Italy annexed Venezia Euganea in 1866,[4] following the Third Italian War of Independence and a controversial plebiscite (see Venetian nationalism); Julian Venetia and Venezia Tridentina passed under the Italian rule in 1919, following the end of World War I.

Nowadays the name Triveneto includes the three administrative regions of Veneto, Friuli-Venezia Giulia and Trentino-Alto Adige/Südtirol Venetia et Histria, an old region of Italy at the time of Roman Empire, refers to Veneto, Trentino, Friuli-Venezia Giulia, East Lombardy and Istria; it was named after the people of Veneti, who inhabited that region, and who are still largely the main ethnic group of the Italian area (other main ethnic groups include Friulani in the east, mostly in Udine province; Ladins in the Dolomites are between Veneto and Trentino-Alto Adige/Südtirol; Germans in South Tyrol; and Slovene minorities on the border with Slovenia and in the city of Trieste); while after 1947 Venetian/Istrian Italians are just a minority in Slovenian and Croatian Istria.

Roman Venetia et Histria was originally created by Augustus as the tenth regio in 7 AD alongside the nine other regiones.

Its capital was at Aquileia, and it stretched geographically from the Arsia River in the east in what is now Croatia to the Abdua in the current Italian region of Lombardy and from the Alps to the Adriatic Sea.

It borders to the north with Austria and Switzerland, to the east with Slovenia, to the south with Liguria, Tuscany, Marche and the small state of San Marino, to the west with Lombardy and for a very short stretch with Piedmont.