The origin of Castrum Flastrae dates back to the eleventh century: it had an area of 21,000 square meters, solid walls with towers and inside them the tower. The inhabitants of the valley took refuge here during the barbarian invasions.

In 1259 the castle was bought by the family Magalotti, Earls of the castles scattered throughout the territory.

Later it was ruled by the Da Varano, then by the Sforza and then back to the Da Varano until 1447 when it came to the Church. The river Fiastra was later called Fiastrone to the impetuosity of its waters in spring and winter. Today it is a spread municipality, based in Trebbio (732 mt above sea level), which includes various castles of great landscape value between mountains and forests on the banks of the lake. Fiastra is located inside the National Park of Monti Sibillini.

The Park Visitor Center houses the Museum of Suede and throughout the year it is in charge of environmental education for schools and adult groups. Near Fiastra and the lake there are many possible excursions to discover the natural beauty of the place, like the one to the Gorges of Fiastrone.