The basics of the optical telegraph are relatively simple. You stand in a tower and perform an action which can be seen by a person in another tower. That action is translated into a message, which can then be routed to another tower until it reaches its intended recipient.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.