Bridges presentation
had real structural value. On both the Longdon-on-Tern (1796) and the Pontcysyllte (1805)
aqueducts, the cast-iron sections that formed the side walls of the trunk were wedge-shaped,
behaving like the voussoirs of a stone-arch bridge and bolted through flanges. Telford's most
ambitious notion, however, was his proposal of 1800 for a single cast-iron arch of 600ft (183m) span
over the Thames to replace Old London Bridge. An earlier proposal was unveiled in France by
Montpetit in 1779 for a bridge of 400ft (122m) over the Seine, thought to have been the inspiration
for Telford's idea. Even the young United States got into the act when Thomas Paine, the political
philosopher, proposed an iron arch of 400ft span over the Schuylkill in Philadelphia. But the next
most outstanding achievement after Coalbrookdale was the cast-iron arch over the River Wear at
Sunderland (UK), because it actually was built. Completed in 1796 by Thomas Wilson, the bridge
annaabi.ee 
