Entry Requirement
 

We are US citizens and will be taking the 4-night cruise from Rome to Barcelona. We will be in Rome for 5 days pre-cruise and then 4 nights in Barcelona post-cruise. My questions is, do we have to clear some sort of immigration in order to stay in Barcelona for the 4-nights, or we can just walk off the boat (as if going on excursions), with out suitcases since already would have clear immigration when we landed at FCO.

You'll be cleared when you disembark. There will be immigration/customs at the cruise terminal.