Ruston and Hornsby traction engine, 1920.

Traction engines are mobile steam-powered road vehicles which can be used for haulage, agricultural purposes, or as a mobile power source. The earliest portable steam engines were not self-propelled but had to be pulled by teams of horses. Cornish mining engineer Richard Trevithick built the first self-moving steam engine in Britain, but it was not until the middle of the 19th century that makers such as Ransomes and Aveling began to produce them with any real commercial succes. By the end of the 19th century, traction engines were being put to use on many farms. This seven hp single cylinder traction engine was made by Ruston and Hornsby of Lincoln in 1920.