Terence Eden asks why the Romans didn't invent the internet:
What I find interesting is that there was nothing fundamentally to stop the Romans - or any other ancient civilization - from creating such a network. The Greeks experimented with it in 4BCE but it seems it never really caught on. Tower building is easy, as is flag waving or other mechanical forms of signalling. Their technology was certainly capable of building a proto-Internet. That would have had some profound changes to our history.
It's an interesting counterfactual, but I think the better answer is that the Romans did invent the internet in a manner of speaking. The Roman road network was an incredible innovation for its time. Thanks to the ORBIS project at Stanford, we can gain a better appreciation for how significantly Roman roads reduced the cost and time required to travel. Robert Gonzalez describes how many variables you can manipulate in the simulations:
Tell us, would you like to travel to Rome by road, river or open sea? Would you stick to the coasts or set a course through the mainland? During which month would you journey? Would you opt for the fastest route (bearing in mind that the shortest course does not always translate to the quickest passage) or the cheapest? Speaking of expenses, how much would this journey cost you, anyway? (Please give your answer in denarii.)
You can try the interactive maps for yourself here.