Evolution of bridges in the 18th century.

This catalogue lists all the bridges built before 1750 (William Roy’s map), that is, before the modern era. That year was chosen, in part, because in the middle of the eighteenth century, a sea-change occurred in the development of bridge-building.

Prior to 1750, bridges were built largely to save lives. It was not only the frequent drownings that focussed attention, but also the exposure suffered while waiting for days, for a spate to die down in winter, and the hypothermia from soaked clothing that followed any forded crossing. We know very little about the actual bridge-builders, or about those who conceived and paid for the work.  Frequently, we cannot be certain that there was any real design or planning involved. The absence of documentation rather suggests that master-masons improvised, albeit with a great deal of experience and a knowledge of general principles and proportions.

This all changed after 1750. Bridges were now built to improve trade, travel and economic development rather than to save lives, and they became an essential component  of the progress of the Industrial and Agricultural Revolutions. The building of London’s Westminster Bridge, completed in 1750, perhaps heralded this new approach. Planning committees were now appointed by councils or government, for all the bigger bridges; meticulous plans were submitted, discussed and compared; and calculations of design, flow and pier obstruction were presented, sometimes along with elucidations of the physics of arches. The quality of the stonework improved enormously, and ashlar slowly became the norm. Standards of construction rose, and the attention to detail was of a different order.  The bridges became larger, more horizontal and significantly wider, this to accommodate two way traffic; they also became more decorative.   

We also know the names of many of the bridge-builders from the later period and can list their other achievements.  Master-masons evolved into Masters of Works, often competing with architects, who kept their hands clean. Labelye, who designed Westminster Bridge,  was the first to be termed an 'engineer'.  By 1790, all bridge-architects were calling themselves engineers, and Thomas Telford became the first president of the Institution of Civil Engineers in 1818.   

This takes us into the era of the great names of Scottish bridge building - John Smeaton (Kenmore, Perth and Banff, Coldstream), John Rennie (Kelso, Musselburgh, New Galloway and Newton Stewart), Alexander Stevens ( Hyndford, Ayr, Ancrum, Roxburgh),  and of course from Thomas Telford himself, who, in addition to remotely overseeing some 1000 Parliamentary bridges, found time to build 30 more to his own personal design including Dean Bridge in Edinburgh, Potarch Bridge, Tongland, Dunkeld, Lothian and Bonar.

Finally, in contrast, it is rather astonishing that so many bridges still survive from the earlier period, before 1750.  This fact has always troubled engineers who, when presenting new theories of the physics of arches, often struggled to explain why so many crudely built earlier structures had survived for so many centuries, despite little apparent adherence to such principles.  

Page last updated Dec. '25