Addressing local authorities during a one-day visit to the world's oldest surviving republic, Leo reflected on the legacy of saints Marino and Leone, whom he credited with helping create a society rooted in freedom, mutual respect and community.
The Pope said the two saints translated the Christian message into "a new community and political model, strongly characterised by the Christian principles of freedom, mutual respect and communion", a legacy that he said continues to shape the republic today.
San Marino, a nation of about 35,000 people completely surrounded by the Italian state, traces its origins to the fourth century.
It is governed by a 60-member parliament that elects two captains regent every six months to serve jointly as heads of state, a power-sharing arrangement designed to prevent the concentration of authority.
Using the micro state as an example, Leo argued that small political communities could offer lessons in public service and social cohesion at a time of growing division and distrust.
Leo is the third pope to visit San Marino, after St John Paul II visited in 1982 and Pope Benedict XVI came in 2011.
The American pontiff praised a society "built on respect for one's own freedom and that of others and above all on respect for the sacred Will of God".
He warned that modern societies faced increasing threats from violence, social fragmentation and ideologies that put self-interest ahead of the common good, and urged Christians to respond through forgiveness, solidarity and concern for the vulnerable.
Leo also described San Marino as a "laboratory of good politics" and called for public life to uphold the dignity of every human person "from conception to natural death" - language commonly used by Vatican officials and Catholic leaders when referring to church opposition to abortion and euthanasia.
In 2021, San Marino voters approved a referendum legalising abortion during the first 12 weeks of pregnancy, overturning a decades-old ban.
While Leo did not directly address the referendum, he repeatedly stressed the need for political, social and economic systems to place human dignity at their centre.
