Alexander Stevens was born in Scotland in 1730. He probably trained as a mason but, by 1775 he was also the largest tenant farmer on Adam Gordon’s estate at Prestonhall, Midlothian. Around 1773, a new bridge was built over the River Clyde at Hynford where Stevens was the contractor and probably the designer. This bridge had five arches and cutwaters similar to those used largely in France. In 1784 he built a bridge at Ancrum over the River Teviot and this bridge is probably considered his finest work of architecture. It consists of three spans of average 5.85m (19 ft), rather low rise arch rings and finished in pink sandstone.
Stevens training as a craftsman is apparent in all his bridges with the ornaments and decorations on the finished faces. His work also highlights that he kept himself informed of the latest techniques in bridge building.
From 1784 to 1796 he designed and constructed many bridges which are still in existence today, such as the Bridge of Dun (1785/7), Bridge at Ayr (1786) and Tivot Bridge (1795). In 1794 a construction firm Alexander Stevens & Son built a timber bridge across the tidal zone of the South Esk.
Between 1791-1793 Stevens travelled to Dublin where he designed and constructed a single arch span (31.7m / 104 ft) bridge called Sarah’s Bridge, over the River Liffey in Dublin. It is not similar to his previous designs, but was the longest arch span bridge in Ireland, until the construction of Lucan Bridge in 1816 located upriver on the River Liffey.
Stevens’s largest contract was not designed by himself but by his friend John Rennie. It was the Lune Aqueduct, which carries the Lancaster Canal over the River Lune in Lancashire on five stone arches. It was completed in 1797.
Stevens died in 1796 and the aqueduct was finished by his son, Alexander Stevens Junior.