Pope Francis has crossed the Tiber River for a visit to Rome's city hall, paying homage to an ancient city that integrated diverse peoples over centuries of its existence.

During his visit to the Rome's City Hall on Tuesday, Francis said that "Rome, over its nearly 2,800 years of history, has been able to welcome and integrate different populations and people from all over the world ... without humiliating or crushing their respective peculiar characteristics and identity."

He also warned against letting the Eternal City become degraded now.

Rome is struggling with problems of garbage removal, potholed streets and other issues of decay that have worsened on the watch of Mayor Virginia Raggi, who welcomed him to the Capitoline Hill, where city hall is located.