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,[2][3][4][5] while it was not until the early 20th century that masonry bridges with larger openings were constructed.[6]
The Trezzo Bridge was built between 1370 and 1377 by order of the lord of Milan Bernabò Visconti.[2] Fortified with towers, it provided access to the Visconti Castle high above the Adda.[2] During a siege in 1416, the condottiero Carmagnola deliberately caused the structure to collapse by weakening one of its abutments.[2]
Its single arch featured a span of 72 metres (236 ft),[2][3][4][7] according to other sources even as much as 76 m (249 ft).[8] By comparison, the second largest pre-industrial bridge vault, the French Pont de Vieille-Brioude, spans 45 m (148 ft).[2] The rise of the segmental arch was ca. 21 m (69 ft), with a span-to-rise ratio of 3.3:1.[2] The arch rip, measured at the springing, was 2.25 m (7.4 ft) thick,[2] corresponding to a favourable ratio of rib thickness to clear span of only 1/32. The sandstone bridge was almost 9 m (30 ft) wide.[2] Today, the two abutments with overhanging remnants of the arch vault are all that remain.[2]
The Trezzo Bridge was not matched until the metal Wearmouth Bridge of the same span was built at Sunderland, England, in 1796.[9] Longer masonry arch spans were not achieved until the 1903 Adolphe Bridge in Luxembourg.[6]
