How much time to get from Fiumicino Airport to the port of Civitavecchia?

It's about one hour 40 minutes by bus, you can check Cotral schedules online or get tranfer info from your cruise line. There seem to be six buses per day from Fiumicino.

I really like SAS. I've used them to RT to Venice. New A330 aircraft across the Atlantic. Transfers in Copenhagen are pretty pain free.

Sharon, if your ship leaves that day I would definitely plan to fly in a day early. We just got back from a Europe trip, and both my sister [flying from SFO] and I had problems with our departure. She ended up spending a night in Salt Lake city and arrived in Paris a day late. We [from DC] were able to switch to an earlier flight when our original flight got delayed and would have caused us to miss the connection. I had checked that there were several later flights from Munich to Paris since it was planned as a fairly tight connection... but according to United there were no seats on any of the later MUC-CDG flights. It wasn't a big deal for us since we weren't catching a ship, but think about how much trouble it would be if you got delayed by a day. Good luck!

I have flown SFO to CPH to Italy with SAS and liked it a lot. The transfer at CPH is the best part. Better than most hubs. The bad part is the outrageous high cost of Scandinavia. Nevertheless, you should try to arrange a 3 night layover in Copenhagen on the way back. The city is gorgeous, albeit expensive.
If worse comes to worst you can always get a private car or taxi from FCO to CIV. It's over €100 but they'll get you there in 40 minutes.

If you have never been on a cruise before, you may not know how crowded and borderline unpleasant the check-in procedures can be - partly depending on the size of the ship. It is a false economy to fly in within five hours of the ship's departure. I presume you're taking a cruise partly because you're not keen on "independent travel". But the advice to visit Copenhagen (based on your likely air routing, not because it's the only possibility for such a visit) is excellent.

When we took a cruise from "Rome" to Barcelona a few years ago, we cheerfully spent three nights in Rome. Because we stayed three nights, our hotel (no more expensive than a US hotel), Inn at the Spanish Steps paid for our private car service to Civittavechia. It all depends on how you want to travel. In 2014, we finally got around to Southern Italy. But we cheerfully spent another three nights in Rome (different hotel) before flying home. It was our third time in Rome.

Another alternative is to buy the air from the cruise company. While that gives up a lot of control over the routing, it may (check the fine print ... ) include an obligation for them to get you onto the boat. Note that most cruise company air requests have a disclosure that THEY have the right to make you overnight at your own expense if the air routing requires it. You have to take your travel agent's advice on that probability. Sometimes there is a cruise/air deal you might take, once you have an idea of theprivately purchased air pricing. A final issue is to consider how wrung-out you may feel after the air routing you quote in the OP?

Bad idea. You cannot do it. Lets look at your potential time assuming you do not take shuttle from cruise ship.

Arr Rome 10.30 - assuming everything is on time. Since you are on a cruise most people will have checked luggage.
Arr Airport train station - 11.30 Need to get luggage, use restrooms, walk to train station, buy tickets.

11.30 - Noon Board local train to San Pietro Station. Trains run every 30 minutes but you might just miss it and have to wait 30 minutes.

Arr San Pietro Noon to 12.30. Transfer to train to Civit..... Trains run about every 20 - 30 minutes to Civit and take an hour. Again you might just miss the next train.

Lv San Pietro 12.30 to 1 pm.

Arr Civit.. 1.30 to 2.00 It is about a 20 minute walk to your ship's shuttle just inside the port entrance. There are taxis and a local bus available at the station but the taxi do not like a five minute fare and it is a small local bus making the loop to the port so walking is often quicker.

So you could arrive at your ship's check in point as late as 2.30 but check in will be quick since most people will be on board by that time. And you might get there as early as 1.30 but the point is you have no margin for delay anywhere. If you flight is delayed, your luggage is late arriving, miss a train, etc., you will miss the ship. Since you are an independent traveler the ship will not wait for you.

You have to come in a day early. We always go three or four days early just to make it more relaxing.

Side note - many posters on this site will rip on your decision about a cruise. Taking a cruise partly because you're not keen on "independent travel" has nothing to do with taking a cruise. You can be just as independent with a cruise as traveling via train. In fact cruising can be a very economical way to see a lot of Europe conveniently.

Have you booked your cruise yet? Depending on the cruise line you will be given an embarkation time. I did a cruise this summer leaving Civitavecchia at 8.30 at night. My embarkation time was 2.30 - 3.30. Because I arrived early I was through the embarkation process quickly but it still took a good half-hour by the time I filled out the health questionnaire, had my photo taken for my boarding card/stateroom key, baggage checked through security and so on. At 5.00 once everyone was on board, we were given the all important safety briefing - do not miss this. For late arrivals there was a further briefing before we left port.

FCO is a spread out airport and it is quite a long haul from the plane to the baggage hall. If you checked your baggage on your flight you can wait for up to an hour for it to arrive at the baggage carousel, There is also usually a wait at Immigration. I think you need to allow at least 1.5 hours to get out of the airport. I had carry-on and it was a good 50 minutes before I was in a taxi and on my way into Rome.

If you decide to come into Rome of the day of the cruise departure, I strongly recommend you arrange for a car to pick you up and take you to the cruise ship terminal (costs about Euro 120). It is much quicker than the train and you are not having to haul your baggage around. The trip by car takes around 1 hour from airport to embarkation hall. Or spend the same amount on a hotel in Rome (or look at staying overnight in Civitavecchia) and take your time to get to the port and board.

To me coming in a day early is not a "just in case" it is a necessity - flight delays, etc can eat up the time and build up your stress - who needs it? And can you imagine what would happen if you were delayed enough that the boat left without you? Why risk it? I took three nights in Rome before my cruise, caught up with sleep and enjoyed a couple of days in Rome and arrived at my ship ready to enjoy a relaxing Adriatic cruise.