What was used to power the first locomotives?

Richard Trevithick, a British mining engineer and inventor, built the first train in 1804. The train was powered by a steam engine with a large flywheel to even the piston rod action, giving the world the first machine that could carry a large number of people and goods. In 1698, Thomas Savery invented the steam engine. However, the first steam engine was low-powered, so it could not be used for powering trains. Then, in 1763, James Watt developed a crankshaft that converted steam power to achieve circular motion. His invention led to the creation of steam-powered locomotives and steamships.

Source: Unival Logistics