Signal-Stations, Lighthouses and Fortlets
The ancients were well acquainted with the art of transmitting news by means of visible signals. As early as 458 B.C. Aeschylus could the news of the fall of Troy as conveyed to Greece by a chain of beacons and in the second century B.C. Polybius describes actual Roman methods of sending elaborate messages by light-signals. In the fourth A.D. the military writer Vegetius mentions fire, smoke and semaphore codes as employable for signalling.
Archaeological evidence confirms the general sense of these statements. Early in the second century the signal-towers of the Danube frontier are sculptured on Trajan's Column. They are wooden towers two storeys high, protected by palisades; the thatched upper storey has a balcony, and from its window projects a torch for sending fire-signals, exaggerated in size in order to show it clearly. Next to the towers are seen beacons for more prolonged and general alarms, comprising log-beacons and straw-flares. Later in the same century the towers of the same frontier are again represented on the Column of Marcus. They have undergone a certain development. They are now, sometimes at least, built of stone and provided with roofs of tile instead of thatch; the palisade round them has become stouter, and the opening in it is closed by a gate.
Outside Britain excavation has revealed large numbers of such structures along the German frontier, where something like a thousand towers are reckoned to have been in use. There two kinds of tower recognized. First, there is the wooden tower, with a post-hole corner, surrounded by a circular mound and ditch. In the mound, and sometimes in the ditch, traces of a surrounding palisade recovered. Secondly, there is the stone tower, a building generally 20 feet square externally, though occasionally polygonal. Their relationship makes it clear that the wooden towers were replaced by stone ones.
In Britain numerous types of signal-stations have been identified. The earliest known are the Old Burrow and Martinhoe on the coast of Devon, which are dated to about A.D. 50-60. Old Burrows appears to have been a short-lived work in which permanent buildings were not erected. But Martinhoe contained a centuria of men, housed in timber buildings. Their position indicates coastwise signalling, at the means employed for transmission are not known. Their ramparts and ditch enclose an area about 80 feet square, with a very widely spaced outer ditch beyond, perhaps enclosing beacon stances.