It’s the most important Benedictine Monastery of our territory. Some scholars (Benedettoni, Bellenghi) accepted the tradition that it was originally a roman temple, later transformed in Christian church; but the hypothesis is unfounded. Church and monastery rose in the last decade of 10th century from the initiative of a society of secular vassals, who, in the early decades of the following century rendered it autonomous. It reached the main importance and power in 13th century, when governed more than forty churches, feudal castles, land properties, in the territory of Fabriano, Genga, Sassoferrato, Roccacontrada. It declined in 14th century, during the Simony and mundane government of abbot Crescenzio (1308-1348). In 1406 Chiavello Chiavelli obtained from the pope the suppression of the castle and admitted it to the monastery of Saint Catherine of Fabriano. Fallen to the rank of rural shed, it became church of Saint Sebastian of Pierosara , with attached cemetery.
There is no clue that the church be a restructuring of a roman temple, presenting all the features of medieval sacred building. The church, after the restructuring of this century,The church, after the restructuring of this century, appears as a genuine Romanesque building, which recalls palaeochristian architectonic particulars, as well as Lombard and Byzantine. It is perhaps the most important Romanesque building of Marches. The walls are made of travertine bricks and mixed materials ; the plant is admirably simple, geometrically harmonious, the dome is elegant and slender.
