Romans had bloomery-made wrought iron only, which was a hand-made process of uneven quality, and made only in small batches. The role of carbon (and how to intr

Romans had bloomery-made wrought iron only, which was a hand-made process of uneven quality, and made only in small batches. The role of carbon (and how to introduce it) was only vaguely known, so quality would vary. It would be quite difficult to make a boiler with bloomery iron. The blast furnace only showed up around 1100. The Romans could certainly have made a Newcomen-style low-pressure steam engine; the first boilers were made of lead and copper (though they quickly switched to iron). However, those are of only mild usefulness. Perhaps they would have found employment in the Roman world in the same place they did historically: de-watering mines. However, it would have to compete with slaves and mules, and there's not a lot of coal in the Mediterranean world, so fuel costs would be substantial, especially for such an inefficient device. A more useful high-pressure Watt style engine could perhaps be made of bronze, but the cost would be fairly astronomical. The Romans could pay it, of course, if they wanted to; huge quantities of bronze would be used in ship rams and statues. But they didn't know they could, and it's uncertain that they'd want to if they did.