The site of Castelletto Monastero, in the diocese of Vercelli, stands on the boundary between the modern provinces of Biella and Vercelli on the edge of a “baraggia” terrace (a geological formation of alluvial origin, covered by wasteland with spontaneous vegetation) where the Cervo and Ostola torrents meet. The area, occupied from at least the Roman period – as attested by evidence of burials and settlement – was crossed in antiquity by a network of tracks linking the upper Vercelli plain with the alpine areas of Biella and the Valsesia. These tracks were also used, at least in the medieval period, for transhumance.

A Cluniac priory stood on the site, first mentioned in a document of 1092, although there is mention in 1083 of the Burgundian abbey at Castelletto, which owned estates in this area. The foundation of the monastery was also linked to a dynasty of functionaries, the counts of Pombia (later Biandrate) who, between the 11th-12th century, increased their presence in these territories and consolidated their power.

Today the area still preserves standing remains of the monastic complex, visible in the church of SS. Pietro e Paolo (transformed into a parish church in 1593, after the priory’s suppression) and in a number of related structures, in particular: a forepart abutting the church façade, its earliest phases probably dating to the 12th century; the orthogonal structure to the church itself, part of the cloistered area; a building east of the church and parallel to it, probably the second church of the priory following the Cluniac model.

During the summer of 2009 the Dipartimento di Studi Umanistici undertook a first excavation campaign in the courtyard area which opened along the south side of the church, over a surface area of circa 275 m2. When the surface deposit had been removed numerous walls appeared mostly on a parallel and orthogonal alignment to the church’s south wall. Around the end of the 18th-beginning of the 19th century all were razed to a uniform height (circa 15 cm below present ground level) when a cobbled paving was laid.

Almost the entire area was covered by an earth dump, between 30 and 50 cm deep, which sealed the ancient stratigraphy. The upper levels of this stratigraphy were exposed at the end of the campaign, following the removal of the dump and will be investigated during the next excavation. The numerous pottery fragments found in secondary depositions within the dump dated mainly to the late medieval and early modern periods and probably relate to the phases exposed and not damaged by the late 18th century interventions.

The emerging walls were almost exclusively built with cobbles, some placed in a herring-bone pattern, bonded with mortar. However, other construction techniques were seen in a square room built of cobbles bonded with clay, its corners reinforced with brick, and a brick wall bonded with earth forming the northern limit of a floor in hollow clay tiles. The latter was very well preserved and was only partially exposed as it extended to the south beyond the excavation edge.

For the moment the walls, although they cannot be related to specific buildings, document a fairly well organised layout in the area probably occupied by the cloistered structures, with a diachronic development attested by the diverse phases visible in the walls themselves. This is of particular interest due to the lack of documentary evidence for the layout of the complex (sectors not destined for cult use) until the 19th century.