There was no single first engine
Asking who built the first steam engine has no tidy answer, because it depends on what counts as an engine. If it means any device moved by steam, the oldest example is an aeolipile, a small spinning steam toy described by Hero of Alexandria in the first century CE. It showed that steam could produce motion, but it did no useful work and was not developed further. If it means a machine that did practical work, the usual starting point is around 1700 in England. Even then, the engines had several contributors who built on each other’s ideas.
Ideas before the engine
In the 1600s, scientists learned that air has weight and that a vacuum can be created. Experiments by Evangelista Torricelli, Otto von Guericke and Robert Boyle, among others, showed that atmospheric pressure could push on a piston when the air under it was removed. Denis Papin, a French physicist who worked in England, proposed in around 1690 that steam could be condensed under a piston in a cylinder to form a vacuum and drive the piston down. He built working models but did not turn them into a full-scale pumping engine. These pieces were available to the people who followed.
Savery’s pump
Thomas Savery, an English military engineer and inventor, patented a “fire engine” for raising water in 1698. His machine had no moving piston. Steam filled a closed vessel, was cooled to condense, and the resulting partial vacuum pulled water up a pipe from below. Steam under pressure was then used to push the water higher. Savery promoted the device as the “Miner’s Friend”, but it had limits. Suction can only lift water a modest height, and pushing with high-pressure steam was dangerous with the boilers and joints of the time. Savery engines were used for some purposes such as supplying water to country houses, but were not reliable for deep mines.
Newcomen’s atmospheric engine
Thomas Newcomen, an ironmonger and Baptist lay preacher from Dartmouth in Devon, developed a different design with his associate John Calley. The commonly cited date for the first successful installation is 1712, at a coal mine near Dudley Castle in Staffordshire, though some records and dates are uncertain.
The design used a cylinder with a piston, connected by a rocking beam to a pump rod. Steam from a low-pressure boiler filled the cylinder, pushing the piston up with the help of the weight of the pump rods. Cold water was then sprayed into the cylinder, condensing the steam and creating a partial vacuum. The weight of the atmosphere pushed the piston down, pulling the beam and working the pump. The steam itself did not push the piston; the vacuum and outside air did. That is why this type is known as an atmospheric engine.
Why it mattered
Newcomen engines could drain mines much deeper than horses or water wheels could manage. They were large, slow and used a great deal of coal, since the cylinder was heated by steam and then cooled by water on every stroke. Even so, where coal was cheap at the pithead they paid for themselves. By the middle of the 1700s, engines of this type were working in Britain and in mines elsewhere in Europe, and the design stayed in use for decades after more efficient types existed. Improvements by John Smeaton in the 1760s raised the efficiency of some Newcomen engines through better proportions and construction.
Savery held a broad patent that covered raising water by fire, and Newcomen’s partners are said to have worked under it, so the two inventions were commercially linked. This is one reason the relationship between them is often described as joint rather than competitive.
What happened next
The main weakness of the Newcomen engine, wasting heat by cooling the cylinder each stroke, led to Watt’s work in the 1760s. Watt did not invent the steam engine, and it is a common simplification to say he did. He was repairing a model Newcomen engine when he began to work on improving it. Other claimed early engines, such as 1500s or 1600s devices described in various books, are too poorly documented to treat as established. Pointing to Hero, Papin, Savery and Newcomen as steps in a sequence is more accurate than naming one inventor. Each shaped the next, and Newcomen’s engine is the one that stands as the first widely used, commercially successful steam engine.