While a road now leads up to the sanctuary, it is also possible to reach it by traversing a long (3.5 km) monumental roofed arcade (Portico di San Luca) consisting of 666 arches, which was built in 1674-1793. It was meant to protect the icon as it was paraded up the hill, in an annual procession from the Cathedral of San Pietro. Originally the arches held icons or chapels erected by the patron family. The Sanctuary was meant to house a miraculous icon of the Virgin allegedly painted by Luke the Evangelist.. A church or chapel existed atop the hill for about a thousand years. The present church was constructed in 1723 using designs of Carlo Francesco Dotti. The lateral external tribunes were built by Carlo Francesco's son Giovanni Giacomo using his father's plans. The centrally planned sanctuary has painted artworks by Domenico Pestrini, Donato Creti (2nd chapel on right); Guido Reni (Assumption in 3rd altar on right), Giuseppe Mazza in chapel of St. Anthony of Padua, Vittorio Bigari (frescoes), and Guercino (sacristy). Stucco works are by A. Borelli and G. Calegari and statues by A. Piò.