Trestle bridge

A trestle (sometimes tressel) is a rigid frame used as a support, historically a tripod used both as stools and to support tables at banquets. A trestle bridge is a bridge composed of a number of short spans supported by such frames. Since this type of bridge is sometimes called a "trestle" for short, each supporting frame is generally referred to as a bent. Timber and iron "trestles" (trestle bridges) were extensively used in the 19th century, the former making up from 1 to 3 per cent of the total length of the average railroad. In the 21st century, steel and sometimes concrete trestles are commonly used to bridge particularly deep valleys while timber trestles remain common in certain areas.