Delta Airlines with SkyTeam partners has several cities in Italy on sale from $401 to $450 round trip for travel departures from early December to early May 2017. Most of these deals I checked are via Atlanta or New York with connections in Amsterdam or Paris for Air France/KLM flights to Italy. Florence and Venice are less commonly on sale than Milan. Rome is not on sale.
Delta / Air France Dallas DFW – Atlanta ATL – Paris CDG – Venice VCE – New York JFK – Dallas DFW
Most other dates are in the $440s for Venice.
Delta / Air France / Alitalia
Dallas DFW – Atlanta ATL – Paris CDG – Florence FLR – Rome FCO – New York JFK – Dallas DFW