The Pope said the family was one of the elements of an "authentic and stable culture".
"We must rediscover the family as human beings' most important heritage," he said.
The Pope made the comments during a visit to the city for the seventh World Meeting of Families.
He picked up the theme of families again in an address at the La Scala opera house following a concert in his honour.
The orchestra and choir performed Beethoven's ninth symphony and was conducted by Daniel Barenboim.
"It is in families that we first experience how human beings are not created to live closed in themselves, but in relation with others," he said.
"It is in the family that we understand that self-realisation does not mean being guided by selfishness and putting oneself at the centre, but giving oneself.
"It is in the family that the light of peace begins to burn in people's hearts, so as to illuminate our world."