About the middle of the eighteenth century the work of drainage was at length seriously taken in hand, directed by Fossombroni, the celebrated engineer. “Warps,” or _colmate_, were thrown up at the outlet of each lateral ravine between which the débris carried down from the flanks of the mountains was deposited. The swamps gradually filled up, and the soil became firm. By constructing a dam (_argine_) across the vale at the point chosen for the new water-parting, an outfall was created, and a line of stagnant swamps was thus converted into a pure rivulet. The valley, at one time a hotbed of fever, has now become one of the most salubrious districts of Italy. The newly won lands were at once taken possession of by agriculturists, and 500 square miles were thus added to the productive area of Tuscany. Villages, formerly inhabited by fever-stricken wretches, have become wealthy towns, and the success of this _bonification_, or reclamation, has been thorough. The torrents are under control now, and have already deposited 17,650 million cubic feet of alluvium over an area of 50,000 acres, as if they were intelligent workmen. The same system of drainage has been successfully applied in other parts of Italy, and particularly near Grosseto, on the right bank of the Ombrone. Amongst the great drainage works which will evermore contribute to the glory of Tuscan engineers, the innumerable canals draining the plains of Fucecchio, {246} Pontedera, Pisa, Lucca, Leghorn, and Viareggio, each of which was formerly occupied by its lake, deserve to be noticed. One of the most difficult of these lakes is that of Bientina, or Sesto, to the east of the Pisan hills, which is supposed to have been formed by an overflow of the Serchio. In former times this lake had two effluents, one running north to the Serchio, the other south to the Arno. The outfall left nothing to be desired in ordinary times, but after heavy rains the two effluents were converted into inflowing rivers, and if the sluices had not been closed, the Arno and the Serchio would have rejoined each other in this inland sea. The Bientina, during such freshets, covered six times its ordinary area, and in order to save the fertile fields of Tuscany it became absolutely necessary to create a third effluent. The engineers conceived the happy idea of conveying this new effluent through a tunnel, passing beneath the Arno, three feet in width, into an ancient bed of that river, now supplanted by the Colombrone.