The problem with using bonfires as signals was that the only logical place to put them was at the very pinnacle of each of the mountains that blocked the path of the message. And the problem with that, of course, was that they were very high mountains indeed, which meant that the pinnacles were barren of anything but snow and rock.
And that wasn't even taking the cloud cover into consideration. When the fogs came down – and down they did, a dozen times a week or more – it was all you could do to see your hand in front of your face, much less the next two mountains in the chain. You had to train the young ones to look ahead before they lit the torches and spilled the oil and burned the logs which had been dragged so painfully into place, lest the fire burned itself out before it was seen. The worst stations had tried using horns as signals, but the sound had sent a wall of snow down from half the mountaintops around, destroying the paths to the valleys and home, and the notion had been discarded once they'd managed to dig their way out again.
No, it had to be fires, and once a season the logs had to be tested, though few of them rotted in that high dry air. The oil sometimes thickened in winter, becoming too thick to pour, but no one fretted over that. Only a fool would attack in winter, and even if one did, there'd be no point in sending for reinforcements that couldn't travel fast enough to help.
And once every dozen years they lined up logs and planned a day to test the chain of fire. The old men would come out of their houses to watch, and the young ones would dance below the blazes, rejoicing in the chance to stop waiting for a little while before they had to build the pyres anew.