The Cornish-Windsor Covered Bridge is the longest wooden bridge in the United States and the longest two-span, covered bridge in the world. It is also a classic example of wooden bridge-building in 19th-century America. With copious supplies of timber at hand and a generous reserve of carpentry skills available, bridge builders in early America quickly discarded the masonry arches prevalent in the Old World. Instead, they opted for a revival of timber-truss designs dating from 14th century Europe.
Ithamar A. Beard, an engineer of some prominence in New England, surveyed the mill brook and selected the best site for a storage dam. Contractor Simeon Cobb, knowledgeable of contemporary civil engineering practices, made major changes to the dam's original design, converting the linear dam into a gentle arch.