The Nile begins to increase at the next new moon after the summer solstice, and rises slowly and gradually as the sun passes through the sign of Cancer; it is at its greatest height while the sun is passing through Leo, and it falls as slowly and gradually as it arose while he is passing through the sign of Virgo. It has totally subsided between its banks, as we learn from Herodotus, on the hundredth day, when the sun has entered Libra. While it is rising it has been pronounced criminal for kings or prefects even to sail upon its waters. The measure of its increase is ascertained by means of wells[3538]. Its most desirable height is sixteen cubits[3539]; if the waters do not attain that height, the overflow is not universal; but if they exceed that measure, by their slowness in receding they tend to retard the process of cultivation. In the latter case the time for sowing is lost, in consequence of the moisture of the soil; in the former, the ground is so parched that the seed-time comes to no purpose. The country has reason to make careful note of either extreme. When the water rises to only twelve cubits, it experiences the horrors of famine; when it attains thirteen, hunger is still the result; a rise of fourteen cubits is productive of gladness; a rise of fifteen sets all anxieties at rest; while an increase of sixteen is productive of unbounded transports of joy. The greatest increase known, up to the present time, is that of eighteen cubits, which took place in the time of the Emperor Claudius; the smallest rise was that of five, in the year of the battle of Pharsalia[3540], the river by this prodigy testifying its horror, as it were, at the murder of Pompeius Magnus. When the waters have reached their greatest height, the people open the embankments and admit them to the lands. As each district is left by the waters, the business of sowing commences. This is the only river in existence that emits no vapours[3541].