| Bridge Name: | Trezzo Bridge |
| Image Upright: | 1.5 |
| Crosses: | Adda River |
| Carries: | Two overlapped lanes for pedestrian, horses, carts, and wagons |
| Locale: | Trezzo sull'Adda, Capriate San Gervasio |
| Designer: | unknown |
| Design: | Arch bridge |
| Builder: | Bernabò Visconti |
| Material: | Sandstone |
| Mainspan: | 72.25m (237.04feet) |
| Length: | 72.25m (237.04feet) |
| Width: | 9m (30feet) |
| Height: | 20.7m (67.9feet) intrados |
| Open: | 1377 |
| Closed: | 1416 |
The Trezzo sull'Adda Bridge or Trezzo Bridge was a medieval bridge at Trezzo sull'Adda in Lombardy, Italy, spanning the Adda river. Completed in 1377, the single-arch bridge held the record for the largest span for over four hundred years, until the beginnings of the Industrial Age, while it was not until the early 20th century that masonry bridges with larger openings were constructed.
The Trezzo Bridge was built between 1370 and 1377 by order of the lord of Milan Bernabò Visconti. Fortified with towers, it provided access to the Visconti Castle high above the Adda. During a siege in 1416, the condottiero Carmagnola deliberately caused the structure to collapse by weakening one of its abutments.
Its single arch featured a span of 72m (236feet), according to other sources even as much as 76m (249feet). By comparison, the second largest pre-industrial bridge vault, the French Pont de Vieille-Brioude, spans 45m (148feet). The rise of the segmental arch was ca. 21m (69feet), with a span-to-rise ratio of 3.3:1. The arch rip, measured at the springing, was 2.25m (07.38feet) thick, corresponding to a favourable ratio of rib thickness to clear span of only 1/32. The sandstone bridge was almost 9m (30feet) wide. Today, the two abutments with overhanging remnants of the arch vault are all that remain.
The Trezzo Bridge was not matched until the metal Wearmouth Bridge of the same span was built at Sunderland, England, in 1796. Longer masonry arch spans were not achieved until the 1903 Adolphe Bridge in Luxembourg.