The ''hydraulic telegraph'' of Aeneas

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The ''hydraulic telegraph'' of Aeneas


It was a method through which agreed messages were sent, described by Aeneas Taktikos (4th century B.C.) - in a lost part of his work "Poliorkitica" - and retrieved by Polybius. This method was used as a fast and efficient way of transmitting messages across the vast empire of Alexander the Great.

Messengers stood at carefully chosen hills and used clay or metal cylindrical containers of equal size filled with water. In each container there was a cork floating – a little narrower than the opening of the container. Attached to the floating cork, there was a rod, divided into equal distances, each one bearing an inscription with an agreed message (e.g. "Horsemen have entered the country"). The operator "transmitter" raised a lit torch thus signalling the beginning of the transmission to the other operator "receiver" and then waited for the "receiver" to confirm by raising his torch, too. As soon as the "transmitter" lowered his torch, they simultaneously released the drain plugs of their containers. When the desired message on the rod reached the transmitter's container top (due to the lowering of the water-level in the container), he raised his torch again to signal the other operator "receiver" to stop the discharge of water. The desired message appeared at the container top of the "receiver", as the two containers were identical in size, in diametre of the drains, plugs and water level inside them.

SOURCES: "Polybius, History X, 43-44", "Philon of Byzandium, Syntaxi Michanikis V", "Polyaenos, Stratigimata IV"