"The Great Wall of China had a network of high towers where news of attacks or raids could be passed down the wall by means of lighting a signal fire"
http://www.wisegeek.com/what-is-a-signal-tower.htm
That was also in the Europe too, both before Romans and of course also in their times. Current time Romania's Transylvania for example (Dacia in the Roman's time), is one of the places that was situated at the edge of the Roman Empire. Because of the risk of eastern invasions (migration from east happened all the time), it had an efficient system of fire/smoke outposts signaling the presence of possible enemies over Carpathians, long outside the Roman territory.
Interesting. I hadn't considered the Great Wall. I wonder how often (if at all) it branched? Sending a message down a line should - eventually - lead to sending messages through a network.
That`s exactly what I thought of when reading the article and I expected it to be mentioned at the end. But I only could find your comment here. Well done.