Question about FCO terminals

One ticket or two?

Two. GNV to FCO, FCO to Venice.

Two tickets presents serious concerns.

Checked bags? if so, almost certain to result in failure.

Where does the arriving flight originate?
If it comes from the US you will have to clear passport control, which almost certainly dooms a successful transfer ( even if with only carry-on bags)

2 hours is too tight.
Where does your Delta flight originate? Are you coming from USA?

Delta uses Terminal 3, ITA uses Terminal 1
It's a 5 min walk or so between terminals.
Airport Map
https://www.adr.it/web/aeroporti-di-roma-en/pax-fco-airport-map

If your first flight is even 30 min late- which happens a lot you will not make that flight to Venice.
Will you have checked bags?
If this is first entry to Schengen- you will need to go thru passport control, get your bags recheck your bags then thru security to your next gate/terminal.

Customs will be in Venice and that is nothing more than walking thru correct door.

Have you considered train to Venice?

I believe the OP is originating in Gainsville, FL which means they are connecting either in ATL or JFK (guessing based on where DL has a lot of transatlantic flights from)

Connection in ATL and BOS, actually. If you search Delta BOS to Venice, it actually shows that same flight as part of the itinerary. I am trying to see if maybe Delta will allow a modification to the itinerary without a whole lot of hassle and/or expense. I know it sounds like a complicated itinerary, but I had my reasons and now my reasons have changed.

Worth a try!

ChristineH,

You mention Shengen. Isn't that the same as Customs? If not, what is the difference?

Schengen means you are “entering Schengen area”

https://home-affairs.ec.europa.eu/policies/schengen-borders-and-visa/schengen-area_en

Customs is just declaration of any goods-different than Passport Control or Immigration