Here is the Med-cruise fact that surprises the most people: Rome is not on the sea. The port, Civitavecchia, sits about ninety minutes from the city, which turns a ten-hour port day into roughly six usable Roman hours, and how you spend the transfer decides the day. The ship excursion is the expensive-but-armored option: if traffic strands the bus, the ship waits.

The train is the independent option, frequent, cheap, and about an hour into Rome San Pietro or Termini, but the ship does not wait for a late train, so build in an hour of buffer you hope to waste. With six hours, resist the everything tour. Pick one axis: Vatican and St. Peter's, or Colosseum and the ancient forum, plus one great lunch and the Trevi on the walk between.

Rome rewards depth over checklist here. And if you have already done Rome, Civitavecchia's local seafood lunch beats a fourth sprint through the Sistine.