The Ancient Basilica, the spiritual heart of the Sanctuary, was erected in the 17th century, in the aftermath of the plague of 1599, to fulfill a vow made by the Municipality of Biella. When the church was completed in 1620 a solemn coronation was held, the first of a series that would enrich the history of the Sanctuary every hundred years. The façade, designed by the architect Francesco Conti, whose sober elegance owes much to the green-veined local stone, is embellished by the darker tinge of the doorway, displaying in the upper part the Sabaudian coat of arms of Duke Carlo Emanuele II, sustained by two stone angel. The inscription “O quam beatus, O Beata, quem viderint oculi tui” (O blessed, who will be seen by Your eyes) is carved on the architrave of the doorway. Since the first decade of the 17th century the inscription is the welcoming greeting received by the pilgrim crossing the threshold of the Basilica.
The Basilica, erected on the site of the ancient church of Santa Maria, holds the Eusebian Sacellum, a shrine which dates back to the 9th century. The cupola and the internal walls of the Sacellum display precious frescoes dating back to the 13th century, the work of an unknown artist known as the Master of Oropa. The frescoes, centered on the life of the Virgin and on those saints that were object of particular veneration of the ancient hermitage, are a precious testimony of sacred iconography. The Sacellum holds the statue of the Black Madonna, made of Pinus Cembra or Swiss pinewood, the work of a 13th century woodcarver native of Valle d’Aosta. The blue cape of the Virgin, the vest and the golden hair encircle the black-painted face, whose austere and yet gentle smile has welcomed the pilgrims over the centuries.
According to the tradition the statue was brought to Oropa in the 4th century A.D by Saint Eusebius, who was fleeing Palestine and the fury of the Aryan persecution. In order to grant the diffusion of the Marian cult, Saint Eusebius is said to have hidden the statue amongst the rocks, on the site where the Chapel of Roc nowadays stands. The latter was erected in the first half of the 18th century by the inhabitants of Fontainemore, a village of Valle d’Aosta still connected to the Sanctuary by that ancient procession, which every five years ascends through a winding path the mountains that separate the two valleys. During the restoration works of the Basilica, conducted in 2005, decorations characterized by yellow ochre floral motifs on azure background, dating back to the 17th century, emerged on the vault of the church, unveiling the most recent treasure of a still richly mysterious past.