Which European microstate has the City of San Marino as its capital?

The European microstate with the City of San Marino as its capital is San Marino.

San Marino is a landlocked republic completely surrounded by Italy in the Apennine Mountains. Its capital, officially called the City of San Marino, occupies the summit and slopes of Monte Titano. The city is one of the country’s nine castelli, or municipal districts, and contains landmark government buildings, fortifications, and San Marino Basilica.

San Marino traditionally traces its foundation to AD 301, when Saint Marinus, a Christian stonemason from the island of Rab in the Adriatic, is said to have established a religious community on Monte Titano. The country claims to be the world’s oldest surviving sovereign state and oldest constitutional republic, although the traditional founding date is partly legendary.

A common mix-up is confusing the country with its capital: both are called San Marino, but the capital is specifically the City of San Marino. It is also not the country’s largest settlement; Dogana, in Serravalle, has a larger population.