A short distance from the town of Piagno, in the municipality of Cosio Valtellino, is the ancient abbey of S. Pietro in Vallate, dedicated to Saints Peter, Paul and Maiolo. In a picturesque position, between chestnut and locust trees, in the village of Piagno are the remains of the Cluniac Priory, where you can see the low bell tower, of typical Valtellinese structure, the semicircular apse divided into four sectors and the part of the southern wall of the church, the only remaining parts of the ancient complex. In fact, the Priory, dating back to the 11th century, became a dependency of Piona and then underwent a slow decline that accompanied it until its complete suppression in the Napoleonic era. Of particular beauty are the decorative bands: the plinth with two rows of sawtooth wedges and the soffit with two rows of zigzag wedges and one sawtooth row. In the mighty southern wall there is an opening provided with an architrave, surmounted by a round arch that delimits an originally frescoed lunette. Inside we find the main nave, 20 meters long and 5 wide, while the adjacent space was perhaps an oratory or a chapel.
Excavations have recently been carried out, which have brought to light the walls of what must have been the building used as the residence of the monks.