The San Michele Viaduct, also known as the Calusco or Paderno bridge, is an iron arch bridge, with mixed rail-road traffic, which connects the towns of Paderno d'Adda and Calusco d'Adda crossing a gorge of the Adda river.
A masterpiece recognized as one of the symbols of Italian industrial archeology, designed by the Swiss engineer Jules Röthlisberger, it is 266 meters long and rises 85 meters above the level of the Adda river.
It consists of a single span in iron beams of 150 meters of rope, which supports a scaffolding with two levels of walkability through 7 iron pylons (one railway and the other suitable for vehicles, with a difference in height of 6.3 meters between the two locations).
The roadway is five meters wide and has a single lane, with two pedestrian crossings on the sides. The Seregno-Bergamo railway line passes through the lower level of the bridge, while the carriage road that connects the province of Lecco to that of Bergamo passes on the upper level.
The span is made up of two symmetrical and side-by-side parabolic arches, slightly inclined to each other and with a variable section (more streamlined towards the top). The choice of a single-span bridge, without intermediate supports on the ground, was dictated both by the particular shape of the gorge to be crossed, very narrow and deep, and by the desire not to hinder navigation on the watercourse. The arches lean on concrete and masonry works built in the middle of the walls of the opposite escarpments that descend to the river. The plinths and supporting buttresses are made up of over 5,000 cubic meters of Moltrasio stone and 1,200 cubic meters of Baveno granite.