Hello,
We were on the Freedom in May and traveled from civitavecchia to Rome on the train. It was very easy and about a 45min ride. You can get off at a stop close to the Vatican. You will have to be back on the ship an hour before it sails. There is a bus that will take you from the ship to the outside of the port and then it is a 10 min walk to the train. Buy a round trip ticket for under 6euros. Don't worry about speaking Italian. They will understand what you want at the train station.
There is a subway that is very easy to use in Rome. It goes in two
directions and gets you close to the stops. You can take it from the Vatican to the Forum, the colleseum is right accross the street.
Just remember to get yourself back in time for the ship. I would leave Rome at 4 the latest. It gets very busy on the train after 5.
Will you be able to leave your luggage at the port early?
How did you put your picture in the post?
You might want to look at cruise Critic and see if there is a Roll call for your sailing. You can get lots of helpful hints and may be able to share a private tour. That saves money and you see quite a bit. We had four private tours with a group we met on CC and it saved us a lot.