I believe one will need a shuttle from where the ship docks in Civitavecchia to the port entrance- is this provided by the cruise liner- we're planning to do our excursion into Rome on our own, and not with the ship. Also, when we return, will we find shuttles waiting at the port entrance to take us back to the ship or does one have to find one's own way back. I ask because I hear it's a bit of a distance.
In the port of Civitavecchia, the local port authority provides a free and very nice shuttle service from the ships to the port entrance. You can also grab the free shuttles from the entrance over to the ships. These shuttles are actually large modern buses that run every few minutes. There is plenty of room for luggage and its a great service.