on narrowly missed inventions

Matt writes:

“Your question about which inventions narrowly missed being created earlier reminded me about a little known Greek genius, Heron or Hero of Alexandria. Hero actually built a primitive steam engine. It didn’t start a Roman Industrial Revolution because of the abundance of slave labor. But its interesting to imagine if it did. Perhaps Rome could have extended its rule both in territory size and time. Better transportation would have meant better logistics for the legions. Roman roads then and contemporary Highways now provide a valuable military boon. If the Romans had the means of making railways and trains how different our world would be. Maybe Rome might not have collapsed.”