I am departing on Alitalia how do you know what terminal you depart from? I am going to London Heathrow Apt.,GB and connecting a flight to the US..
Terminal C I think since the UK is not in the Schengen zone. Generally, A is for domestic, B for Schengen flights and C for all other international flights.
John if you travel by train to the airport, there are signs posted at a 'fork' in the walkway/corridor. That will give the information which you need. Alitalia should be able to tell you if you contact them in Rome before you leave.