Hydraulic Telegraph: World's First Telecommunications Device
The hydraulic telegraph, invented by ancient Greeks, allowed the sending of long distance messages as early as the fourth century BC.
It was designed for military purposes by Aeneas Tacticus to send pre-arranged messages across Alexander the Great's empire.
Messages sent included: “Enemy on sight,” “Cavalry attack,” “We need wheat,” “Infantry in action,” “Cyclical movement,” and so on.
Operation of the hydraulic telegraph is described in Aeneas’ work on sieges, Poliorcetika, retrieved by Polybius.
The device was used by ancient Greeks during times of war.
Author's summary: Ancient Greeks invented the hydraulic telegraph.