There were two things our tour guide, Constantine, really wanted us to know as we visited the Acropolis: The Parthenon was built by the citizens of Athens rather than slaves (i.e., as in Rome), and the Elgin marbles belong in Greece.
The Museu d'Historia de Barcelona has excavated miles of Roman ruins of the original city of Barcino, founded by the Romans more than 2000 years ago, under the streets of modern Barcelona.