The arcade 'Portico di San Luca' is the longest in the World (3.5 km) and leads to the Sancuary of the madonna of San Luca some 300 metres above the plain, just south-west of the historical centre of the city of Bologna.
The arcade consists of 666 arches, which was built in 1674-1793.
It was meant to protect the icon as it was paraded up the hill.
A yearly procession from the Cathedral of San Pietro in the centre of Bologna to the Sanctuary goes along this path.
Originally the arches held icons or chapels erected by the patron family.
Source and more informations: Sanctuary of the Madonna di San Luca