Tractors first emerged in the early 19^th century when steam engines on wheels were used to help drive mechanical farm machinery using a flexible belt. The first portable steam engine used for agricultural purposes was invented by Richard Trevithick in 1812 and it was known as the Barn Engine. The Barn Engine was mainly used to drive a corn threshing machine. Advances continued and improvements to engines began to develop as the history of tractors continued. By 1903, Charles W. Hart and Charles H. Parr had successfully built the first American tractor using a two-cylinder gasoline engine. Their firm went on to build 15 farm tractors. Their 14,000-pound tractor is now on display at the Smithsonian National Museum of American History in Washington, D.C. as the oldest surviving internal combustion engine tractor in the United States.