The town's name considers the Latin name "Clasius", to which was added the suffix"-anus "to indicate ownership, while the second part refers to the saint, to whom the most important local church is dedicated. Another school of thought links the town's origins to a temple dedicated to Janus, which was traditionally "clausus", (closed), "clasus Jani". Municipality in the province of Avellino, in the valleys of the rivers Sabato and Calore, it is an excellent trekking starting point for those that desire to reach Monte Tuoro between a local environment, characterized by the lush of chestnut groves, and tidy rows of vines, from which particularly popular wines are produced, such as: Aglianico, Falanghina, Coda di Volpe, Greco and others.
In year 568, Germanic tribes invaded Piedmont and Lombardy and moved also further South, creating a Duchy in Spoleto and one in Campania, in the area of Benevento. Chiusano, which was part of the Principality of Benevento, was equipped with a castle, built in a predominant location to control a wide area of the surrounding territories. The main centre developed around the castle in the XI century. Included in the County of Avellino, it became a stronghold of the Gesualdo, the Del Tufo, the Tomacelli and the Carafa.
- the Church of Santa Maria degli Angeli, of ancient foundation, was built in the XIII century. The current building, with austere forms, is the result of renovations completed in the beginning of the XVII century. It features a Latin cross plan with a dome at the centre. The façade is divided into two floors, topped by a pediment. The structure is flanked by a Bell Tower, massive with a square base, is divided into three frame quadrants that follow the entire perimeter of the buildings;
- the Lombard Castle, located on Mount St. Dominic, in a dominant position. The imposing structure, of which remain part of the walls, was built by the Lombards for defensive purposes and control of the territory. This population, of Germany origins, around the year 500, conquered large areas of the entire Italian territory. Benevento was the first Lombard Dukedom in Southern Italy, later transformed into Princedom and the fief of Chiusano under its domain. In the XII century the fief was granted to Riccardo of Clusano.