This is a slight advance on beacons with a preconcerted code, but it is still quite indefinite.
For it is evident that it is neither possible to foresee all contingencies, or even if one did to write them all on the rod. So that when circumstances produce some unexpected event, it is evident that it cannot be conveyed by this plan. Again none of the things written on the rod are defined statements, for it is impossible to indicate how many infantry are coming and to what part of the country, or how many ships or how much corn.
For it is impossible to agree beforehand about things of which one cannot be aware before they happen.
And this is the vital matter; for how can anyone consider how to render assistance if he does not know how many of the enemy have arrived, or where? And how can anyone be of good cheer or the reverse, or in fact think of anything at all, if he does not understand how many ships are how much corn has arrived from the allies?
The most recent method, devised by Cleoxenus and Democleitus and perfected by myself, is quite definite and capable of dispatching with accuracy every kind of urgent messages, but in practice it requires care and exact attention.
It is as follows: We take the alphabet and divide it into five parts, each consisting of five letters. There is one letter less in the last division, but this makes no practical difference.
Each of the two parties who are about signal to each other must now get ready five tablets and write one division of the alphabet on each tablet, and then come to an agreement that the man who is going to signal is in the first place to raise two torches and wait until the other replies by doing the same.
This is for the purpose of conveying to each other that they are both at attention.
These torches having been lowered the dispatcher of the message will now raise the first set of torches on the left side indicating which tablet is to be consulted, i.e. one torch if it is the first, two if it is the second, and so on.
Next he will raise the second set on the right on the same principle to indicate what letter of the tablet the receiver should write down.
Walbank Commentary