User blog comment:Sparkly Venice/I've got an idea for a new timeline!/@comment-3218619-20150412132903

All the technology was there to make a steam engine by the time of the Romans - the Romans were far more advanced than the Greeks at their respective heights. The problem was materials. Without a way to make a steel/iron engine, a steam engine was a complete impossibility, and one cannot simply handwave them large quantities of steel and the instructions on how to manufacture it.