The first steam engine by Newcomen could have been built by the Romans, but it was hideously inefficient. There's one at the Henry Ford Museum in Dearborn, Mich

The first steam engine by Newcomen could have been built by the Romans, but it was hideously inefficient. There's one at the Henry Ford Museum in Dearborn, Michigan... it's a 2 1/2 story walking beam engine with a boiler about 8 foot in diameter, all working at NO pressure, and riveted together. Rated horsepower? 11 The steam was taken in a wide pipe and allowed to fill the cylinder (which didn't really have a great seal), and the intake was closed, then cold water sprayed into the cylinder, cooling the steam and condensing it... pulling the beam down, and thus lifting the water from the mine, in a graceful slow teeter-totter motion. The cooling of the cylinder is part of the reason the engine was so inefficient. I have no idea how much coal it took to run that, but given that if it wasn't at the head of a coal mine, all that fuel would have to be hauled by animal cart, it wasn't practical to replace 11 horses with something that used far, far more fuel than the equivalent feed for 11 horses (let's say they're in shifts, so 50 actual horses) Watt couldn't get his improved steam engine to work. The cylinders he had made had gaps of up to an INCH around the piston, and no means of packing he had could contain the steam. It was Wilkinson, who had come up with a boring machine for canon that made a cylinder that was made the gap less than 1/8 of an inch, making it possible to seal in steam, and start to use it under pressure. Once the bored cylinder from Wilkinson was available to Watt, the efficiency of steam engines tripled, and went up from there. That is how steam engines really got going.