To drain the lakes they called the air to their aid. The lakes and marshes were surrounded with dykes, the dykes with canals and an army of windmills; these, putting the suction-pumps in motion, poured the waters into the canals, which conducted them into the rivers and to the sea. Thus vast areas of ground which were buried under water saw the light, and were transformed, as if by enchantment, into fertile plains covered with villages and traversed by roads and canals. In the seventeenth century, in less than forty years, twenty-six lakes were emptied. In Northern Holland alone at the beginning of this century more than six thousand hectares of land were delivered from the waters, in Southern Holland, before 1844, twenty-nine thousand hectares, and in the whole of Holland, from 1500 to 1858, three hundred and fifty-five thousand hectares. By the use of steam pumps instead of windmills, the great undertaking of draining the Lake of Haarlem was completed in thirty-nine months. This lake, which threatened the towns of Haarlem, Amsterdam, and Leyden with raging storms, was forty-four kilometers in circumference. At present the Hollanders are contemplating the prodigious enterprise of draining the Gulf of the Zuyder Zee, which covers a space of more than seven hundred square kilometers. The rivers, another internal enemy of Holland, did not cost less fatigue or fewer sacrifices. Some, like the Rhine, which loses itself in the sand before reaching the ocean, had to be channelled and protected from the tide at their mouths by immense locks; others, like the Meuse, were flanked by large dykes, like those raised to force back the sea; others were turned from their channels. The wandering waters were gathered together, the course of the rivers was regulated, the streams were divided with rigorous precision, and sent in different directions to maintain the equilibrium of the enormous liquid mass,--for the smallest deviation might cause the submersion of whole provinces. In this manner all of the rivers, which originally wandered unrestrained, swamping and devastating the whole country, have been reduced to streams and have become the servants of man.