The Cathedral of Santa Maria and San Marcello is the main place of worship in San Donato Val di Comino and one of the most significant religious buildings in the Val di Comino. Its origins date back to the Middle Ages, when the village began to expand towards the lower part of the settlement, giving rise to a new urban area around the church.

The earliest documentary evidence dates back to the early 14th century, when the church is mentioned in the papal tithes of 1308–1310. During the 16th century, the parish took on an increasingly central role in the religious life of the village, culminating in the unification of the parishes under the title of Santa Maria and San Marcello, decreed in 1569 by Bishop Tommaso Gigli.

The cathedral’s current appearance, however, is primarily the result of major works carried out in the 18th century, when the structure was enlarged and transformed in the Baroque style. The layout was changed to a basilica plan and the façade was embellished with elegant pilasters, attached columns and refined decorations which still today give the building a harmonious and monumental appearance.

The stepped façade is divided into two sections, each decorated with pilasters and half-columns. The lower section features three entrance portals, whilst the upper section is adorned with a central window and crowned by a pediment. Adjacent to the church stands the square stone bell tower, characterised by simple single-lancet windows that lend a sense of lightness to the structure.

The interior of the cathedral comprises three naves separated by pillars with round arches, creating a spacious and elegant space. Among the most important works is the precious pipe organ, attributed by some scholars to Cesare II Catarinozzi, a renowned master nicknamed the ‘Stradivari of the organ’. The instrument retains a classical acoustic design with registers of great value and a refined wooden case.

Beneath the high altar, housed within a glass urn, lies the relic of Saint Constance, transferred to the cathedral in 1756 from the Catacombs of Saint Agnes in Rome. The saint is deeply venerated by the local community and every year, on the last Sunday in August, she is honoured with a solemn procession accompanied by the traditional pottery and onion market.

With its blend of medieval history, Baroque elegance and popular devotion, the Cathedral of Santa Maria and San Marcello remains the spiritual and artistic heart of San Donato Val di Comino to this day.