Here on HN I read about the theory, that one of the main reasons that the time of the steam engines came, was the rise of the cannon. Over generations, every king wanted to have the best cannons as that translated into power - and once you can build a cannon, you can build something that can contain high pressures and give that pressure a direction. In other words, to take that toy further, they would have also had to greatly improve their metallurgy first. Otherwise a smart greek inventor would have just created spectacular (and dangerous) booms, but nothing that could reliable do more work, than a ordinary slave.