I am not sure where you would connect with the Rome subway system but this is how we got around. Rome is small enough in the area around the Forum to walk. We walked from the Spanish steps area to and around the Forum and back to hotel near Spanish steps, A long day but we would stop now and then for a coffee break.. We took the subway to St.Peters in the morning, waited in the long line to get in and found many people just cutting into the line at the place where you get your tickets. Maddening after you have stood in the line for an hour. It's just what they do and nothing you can do about it. Rome was fabulous.