By foot from Civitavecchia (Rome) to Civitavecchia (Rome) (city)
Depending on which pier your cruise ship docks, the walking distance to the port exit will be around 2 to 3,5 km (1,2 to 2,2 miles) to the Largo della Pace information center. Walking is your best and fastest option if you are heading for the train station (train to Rome) and if you are docked at pier nr. 10, 11, 12, 12 bis, 13 or 13 bis.
In all other cases it's better to first use the free shuttle bus service of the Port Authorities. It will bring you to Largo della Pace just outside the harbor. From there you can easily discover Civitavecchia on foot.