In its present condition, the Crau may be divided into two parts, that which is watered, and which has been converted into a garden, and that which is not as yet reached by the rich loamy waters of the Durance, and is therefore parched and desolate, overrun by herds of sheep and cattle, driven down in winter from the Alps, when a certain amount of herbage is found on the desert, which in summer is utterly dry and barren. These migrations date back to a remote epoch, for they are mentioned by Pliny.
Previous to the construction of the canal by Craponne, who began it in 1554, the desert reached to Arles; the whole of the plain south of the chain of the Alpines was either marsh lagoon, or a waste of stones, where now grow and luxuriate mulberries, olives, almond trees and vines. The canal of Craponne was carried by the originator for thirty-three miles, sending out branches at Salon, Eyguières, and elsewhere. In winter the meadows are green as those of Devon in spring, and the fields yield heavy crops. Indeed, the Durance acts to this region in the same way as does the Nile to Egypt. "The meadows I viewed," says Young, "are among the most extraordinary spectacles the world can afford in respect to the amazing contrast between the soil in its natural and in its watered state, covered richly and luxuriantly with clover, chicory, rib-grass, and Avena elatior."
The climate of the Crau presents contrasts most extreme. In winter the thermometer falls and remains below zero for many nights in succession, and the glacial bise sweeps over the face of the desert, curdling the blood; the flocks and herds seek shelter from this blast behind the long walls of dry stones, which sometimes the violence of the wind throws down upon them.
During the summer the phenomenon of the mirage is almost continuous. The bed of air in contact with the surface of stones scorched by the blazing sun becomes rarified and dilated, so that the horizon appears to be fringed on all sides with lakes of rippling water, most deceptive and tantalising to the eye of the traveller.
The troops of wandering bulls and wild horses, flights of rose-coloured flamingoes, of partridges and wild ducks give this region a pronounced oriental physiognomy, and however painful it may be at such a time to traverse this burning plain, it affords a curious picture of the Sahara in miniature nowhere else to be seen in Europe.
The great scourge of the Crau is the north-west wind, the bise, the black boreas of the ancients, so violent as to roll over the pebbles, and to blow away the roofs of houses, and tear up trees by the roots. In fact, the Crau may be regarded as the Home of the Winds.
It is easy to explain the origin of these furious gales, bise and mistral. The low sandy regions at the mouth of the Rhone, denuded of all vegetation, and the great stony plain of the Crau, heated by the direct rays of the sun, rarify the air over the surface of the soil, and this rises, to be at once replaced by the cold air from the Alps and Cevennes; the air off the snow pours down with headlong violence to occupy the vacuum formed by the heated ascending column of air off the plain, sweeping the valley of the Rhone, and reaching its maximum of intensity between Avignon and the sea, where it meets, and is blunted in its force by the equable atmosphere that covers the surface of the Mediterranean.
The violence of the wind is consequently due to the difference of temperature between the hot air of the plain and the cold air of the mountain.
An old saying was to this effect:—
"Parlement, Mistral et Durance
Sont les trois fléaux de Provence."