The present Ashburnham (Hunter Street) Bridge is an eleven-span concrete arch structure spanning the Otonabee River in Peterborough that opened in 1921. Renowned Toronto-based civil engineer Frank Barber (1875–1945) designed the structure with the assistance of W. E. Taylor and F. Christie, and American architect Claude Fayette Bragdon (1866–1946) was responsible for its magnificent aesthetic features. The main open-spandrel arch span of 234 ft. (71.6 m) was the longest concrete arch span in Canada at the time of construction, surpassing the previous record by 56%. The main span arch is unreinforced because Barber specified that the originally constructed three-hinge arch be made monolithic when the air temperature was the average for Peterborough, to minimize thermal stresses, and a concrete placement scheme with infills to minimize the effect of shrinkage. This paper briefly summarizes: the career of Barber, and his strong advocacy of reinforced concrete bridge construction; his mathematically based structural theory that may have been used to analyse the bridge; the state-of-the art of concrete arch bridge construction at the end of World War I; and, the background to, and technical and aesthetic innovations of, the Ashburnham Bridge.