The Most Serene Republic of San Marino is one of the six European microstates, with an area of only 62 sq. km and about 30,000 inhabitants. San Marino was founded in 301 CE by a stonecutter named Marinus of Rab and is said to be the oldest recorded sovereign state and constitutional republic in the world.
The Three Towers of San Marino -- appearing on the flag, coat of arms, and coins -- are located on the three peaks of Monte Titano. They were constructed between the 11th and 14th centuries and are part of the San Marino UNESCO World Heritage site.
While not a member of the European Union, San Marino has special permission to use the Euro with its own designs on the national side of euro coins.
San Marino on Wikipedia