The Early History of Data Networks[Contents] [Previous] [Notes] [Index]

The 2000-Year Gap

It is hard to believe that for almost two millennia people were any less curious about the construction of practical methods for long-distance communication than they were at the time of the Egyptians, Babylonians, Greeks, and Romans, but the sobering fact is that throughout this period only occasional references were made to simple beacon fires or messenger systems. All progress that had been made was forgotten.

We find a first new reference to a telegraphic system in the ninth century It was developed by Leo the Mathematician in Byzantium, during the reign of Theophilus ( 829-842). Francis Dvornik described this system as follows:[Note 105]

He [Leo] constructed two identical clocks which kept exactly the same time. One was placed at the last station of the fire signals near the frontier [in Loulon], and the other near the imperial palace [in Constantinople]. Twelve incidents likely to occur, and which would have to be communicated through seven relays to headquarters at the imperial palace, were assigned to each of the twelve hours and written on the faces of both clocks. Upon receiving intelligence that the enemy was about to cross the frontier, the commander of the frontier post lit his fire signal when the clock showed the hour of one, and thus the watches in the palace knew at what time [day?] the invasion had begun.

Reportedly, this system was used until well into the tenth century To make a system like this work at all, there must have been a method to compensate for the 22-minute time difference between Loulon and Constantinople, and the shortening of the time available for nighttime signaling during the summers. Even with those problems solved, it must have been hard to construct clocks that could be kept in sufficient synchrony, and hard to cope with the average half-day delay before an urgent message could be sent. Considering also the limited code space, it is hard to see this as an improvement over Polybius's system.

Figure 1.9 Sixteenth Century Spanish Map (Detail).
(Source:" "Sider 1992" "Fig. 24)

Three hundred years later we find the following passage in Usatges, a book written by Berengars I in 1176:[Note 106]

When the sovereign is attacked, or when he discovers that a king or monarch advances to fight him, he will inform his constituents either by proclamation, or by messengers, or in the usual way, by fire signals.

The use of the phrase ``in the usual way'' (German: auf die gewohnte Weise) seems to indicate that the use of fire beacons was still the standard way of communicating signs of alarm, victory or attack.

Another three hundred years later there still hadn't been much progress. The text of an enactment of the Scottish Parliament from the year 1455, for instance, reads:[Note 107]

One bale of faggot shall be the notice of the approach of the English in any manner; two bales that they are ``coming indeed;'' and four bales blazing beside each other, to say that they are ``coming in earnest.''

The first sign of improvement came in the early sixteenth century. In this period, the French, Spanish and Venetian navies started using simple flag signaling methods for ship-to-ship and for ship-to-shore communications. Precious little is known about the devices or codes that were used,[Note 108] but on old maps from this period peculiar disc-shaped devices suspended from towers can be seen that in all likelihood served signaling purposes (Figure 1.9). Almost identical signaling devices were used in Holland until well into the nineteenth century.[Note 109]

The improvements in signaling apparently did not spread very rapidly through Europe. In 1569, for instance, the British erected a signal house on a platform battery in Portsmouth, as the endpoint of a classic line of beacons that stretched from Portsmouth to London. It was this line of beacons that notified London of the approach of the Spanish Armada in 1588.[Note 110] If the Spanish did indeed have better signaling methods, it does not seem to have helped them in this instance.

At the start of the seventeenth century a discovery was made that would change the art of signaling decisively.


In 1608 Dutch spectacle-maker Hans Lippershey accidentally aligned two lenses of opposite curvature and of different focal lengths in his workshop in Middelburg. He discovered that this combination of lenses distorts the image in a wonderfully useful way: the telescope was born. Galileo was able to reproduce the effect, based on a description he had received from Holland. By the end of 1609, he had succeeded in building a 30-power telescope, allowing him to discover, for instance, the moons of Jupiter. In 1610 he published his findings in Siderius Nuncius (The Starry Messenger).

The invention of the telescope made a considerable difference in the development of telegraphs. Since large objects could now be spotted from 15 to 30 km (10 to 20 miles) away, it didn't take much imagination for the inventors of those days to consider all kinds of new telegraphic schemes. Some of these systems are referred to in Edelcrantz's treatise, as follows:[Note 111]

Also notable is an idea from an unknown person that is contained in a letter to Schottus. He proposes to establish communication between Mainz and Rome by erecting 5 poles on a hill at such a distance from each other that they can easily be distinguished from 5 to 6 [German] miles away with a telescope. A pulley is attached to the top of each pole to hoist a stick, a sheaf of straw, or other objects to the top. If the alphabet is divided into 5 groups of letters, an object is first raised to indicate the group number. After the first object is lowered, another one is raised to indicate the number of the letter within the group. The art is the same as that of the Greeks but adapted to daytime use. The inventor, however, seems to be the first to have suggested the use of telescopes.

Figure 1.10 Kessler's Device.
(Coll. New York Public Library, New York)

Edelcrantz refers to Gaspard Schottus, who lived from 1608 to 1666. The letter that Schottus quoted in 1664 was written by Philipp Ernst Vegelin von Claerberg, an official at the court of the Prince of Nassau.

Edelcrantz continues with a more interesting reference to a method that even predates the one described by Schottus.

Someone named Kessler, who lived at the beginning of the last century [i.e., the seventeenth century], suggested using letters cut from the bottom of barrels, using them to spell out words that would be readable at great distances.

Someone named Franz Kessler (ca. 1580-1650) did in fact write a book called Unterschiedliche bisshero mehrern Theils Secreta oder Verborgene, Geheime Kunste (Various until now mostly hidden, secret arts), which was published in Oppenheim in September 1616. The description of Kessler's method given by Edelcrantz is not quite accurate, though. Kessler was one of the first authors to describe a working system based on the use of a telescope and a light signaling device.

In the preface to Kessler's book written by Hans Dietrich von Bry, a bookseller from Oppenheim, the method is introduced as follows:[Note 112]

Then it is not a small matter that two good friends in case of emergency, or otherwise at their pleasure, can communicate their wishes to each other, without meeting or go-between, and also at one or two miles distance can have their discourse or conversation, which in case of a siege or in other emergencies can be used to advantage to save an entire city or fortress, as will also be learned in more detail from the [following] description.

Kessler himself then refers to the telescope as a useful novelty from Holland. Apparently the word telescope had not been adopted yet.[Note 113]

With the help of a long perspective, and in recent years in Holland newly discovered Tubular Spectacles [German: Rohren Brillens], used outside in the field, with which one can see best in time of peace, and the most secure at times of war.

Kessler then describes how the alphabet can be compressed into fifteen essential characters, each of which can be associated with a number between one and fifteen in a pre-arranged random order, to make it harder for others to detect what is being signaled. Kessler stresses that the code can and should be changed frequently if secrecy is required.

To use this code, in addition to ``tubular spectacles,'' one needs:[Note 114]

At night a burning light or a torch suffices; by day a mere stick with a white piece of cloth or paper.

Kessler then details the nighttime signaling method. For this one needs:

. . . two square boxes, or common round barrels. They must, however, also on the inside, be covered with lead. In the middle of the barrel one must place a long hook. The bottom of the barrel must have a square door, about a quarter ell [15 cm] long and wide, so that, through this door, one can hang from the hook several pitch-crowns of appropriate size.

The barrel is placed on its side, with the bottom facing the signaler, as illustrated by Kessler in Figure 1.10. The other side is open, but equipped with a shutter that can be lifted or lowered to produce the light signals: one flash for the letter ``d,'' two flashes for an ``i,'' and so on.

Kessler realized well that the same encoding would work for waving a flag, or for giving sound signals with bells, or hammers, or by knocking on walls.[Note 115]

He gives much attention to a related problem, which seems to indicate that, unlike many other inventors from this period, he really did use the signaling method he describes. The question is how one could locate a remote receiver or sender in the middle of the night, before the signaling begins. To solve that problem Kessler built a large disc, marked in degrees from 0 to 360, with a compass on it, and with a pointing device attached to the center. The pointing device was a simple stick with two flat pieces of metal at the ends, each with a small slit in it. The idea was that at daylight one would accurately locate the remote correspondent, mark the angle on the disc, using the compass for an absolute reference of orientation. Then, at night, at a predetermined hour, the barrel and the disc would be lined up with the remote location, and signaling could begin. Curiously, Kessler states that the receiver only really needed the disc, not the barrel, which implied that he had not thought of things like message acknowledgement or error control. The method is reminiscent of signallights flashing Morse codes, as they are used in the Navy even today.

Several less sophisticated methods from the same period seem to have been popular; sufficiently so for the Dutch writer Wynant van Westen to remark in his booklet, Mathematische Vermakelyckheden (Mathematical Amusements), published in Arnhem in 1636, that these signaling devices were of most use to spies, since they made it so much easier to intercept the supposedly secret communications of an adversary.

Mentioned in many sources is a description from the Marquis of Worcester, in his book Century of Inventions, which was published in 1663. He claimed:[Note 116]

. . . a method by which, at a window, as far as [the] eye can discover black from white, a man may hold discourse with his correspondent, without noise made or notice taken; being according to occasion given, or means afforded, ex re nata, and no need of provision beforehand; though much better if foreseen, and course taken by mutual consent of parties.

There is again no mention that a large-scale use of this method was ever contemplated.

Another telegraphic device mentioned by Edelcrantz is a letter telegraph developed by the Englishman Robert Hooke (1635-1703).[Note 117] Hooke's device would prove to be a seminal step in the development of telegraphy. Nonetheless, it appears to have been only of passing interest to Hooke himself.

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The Early History of Data Networks Gerard J.Holzmann, Björn Pehrson
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