Antonelli had been invited to present a new project for the Crucifix Sanctuary in Boca since 1827, but the works proceeded very slowly. The old image of the crucifix, depicted in a small country chapel along the road that connects Maggiora to Grignasco, had been a popular pilgrimage destination for centuries.
In 1820 the architect Giovanni Agnelli was asked to design a series of porches, in order to host the numerous pilgrims. But Antonelli suggests a big, semi-circular porch and a building intervention that would have caused the transformation of the area with a new church.
The works will start only after 1860 and the architect will change his mind about the sanctuary he had conceived in his youth: having no possibility to intervene on the plans any more, since the walls and columns had already been erected, he concentrated on its raising.
The stream that once used to pass through this area and whose course had been already diverted and the rocky hillside would have suffocated the building. As his son Costanzo had said, it would have run the risk to appear as ugly, poor in characteristics”.
That is why he gave emphasis to the sanctuary’s verticality, increasing the temple’s capacity. Among the existing columns he created a corridor that faces the church, from were the pilgrims would assist service. From here a second series of columns makes the ledge reach 25 metres of height, creating a spectacular barrel vault (1871-1877).
At the sides of the vault, Antonelli created the cells that would host the pilgrims. Still not satisfied of the 37 metres reached, he convinced the sanctuary administrators to create above an oratory where to keep the votive offerings. The highest point of the building is 51,32 metres tall. At this point the architect designs an incredible pronaos (24,20 for 15 metres) with eight central columns, of vertiginous height, surrounded by two lateral aisles which connect it with the other porches.
A genius complex even for its shed shaped covering, completed by his son in 1892.
Antonelli’s last project consisted in a further raising of the lateral porches, in order to reach the pronaos height and doubling the corridors above the lateral naves, to increase the sanctuary’s capacity and enlarge it. Two large porches, connected to the pronaos, would transform completely the big space of the sanctuary, connecting it to the first semi-circular porch that surrounded the church.
The pyramid shaped building was then exalted by an incredible, cylindrical belfry, 100 metres tall.
The direction of the works was entrusted to Costanzo, after his father’s death, in order to complete the inside, antonellian decoration.
Although the works were interrupted, they went on up to the terrible collapse dated August 30, 1907 causing the destruction the left wing; the subsidence of the forth column involved nine of the ten spans.
The reconstruction works were initiated in 1912 and concluded in 1918, though Costanzo retired from directing the works in 1915.