A skew arch is a method of construction that enables an arch bridge to span an obstacle at some angle other than a right angle. This results in the faces of the arch not being perpendicular to its abutments and its plan view being a parallelogram, rather than the rectangle that is the plan view of a regular, or "square" arch.
A masonry skew arch bridge photographed shortly after its completion in 1898, showing the helicoidal nature of its stonework. Sickergill Skew Bridge over the River Raven at Renwick, near Penrith.
Store Street Aqueduct from Store Street
Swin Bridge over the River Gaunless
A contemporary engraving of Denbigh Hall Bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct may be made from a series of arches, although other more economical structures are typically used today.
A double-arch stone bridge in Nagasaki, Japan
The Roman Alcántara Bridge, Spain (built 103-106 AD)
The Anji Bridge, 6–7th century AD
Segovia Aqueduct (c. 100 AD)