Again Wizard Ismen speaking to King (Emir) Ducat. According to astrology -- or more simply, weather forecast -- a heavy drought will bring the Crusaders to their knees, but not so with the inhabitants of Jerusalem, because. . .
Né solo intorbidasti i chiari fonti
Ma da marmoree conche e lucide urne,
Con l'industria de' tuoi, che fûr sì pronti
Per molti mesi a l'opere diurne,
Sotto le valli e sotto i cavi monti
Per tenebrose vie, quasi notturne,
In due gran laghi l'acque hai qui condutte,
Di fuor lasciando l'altre parti asciutte.
"Not only did you poison the fresh springs [making them useless for the Crusaders], but, out of marble basins and water tables, thanks to the industriousness of your men who worked hard for many months, day by day, now under the valleys and the mountains through dark channels you gathered the waters in two great lakes, while the surface lands have been left dry."
This was an actual war strategy. But especially, we have here an example of the great interest of the Renaissance in hydraulics, see Leonardo Da Vinci.
On the other hand, important hydraulic systems had been realized in the Holy Land already in the first millennium BC. Many data about this can be found in the detailed German pilgrim's guide Im Land des Herrn (here), of which an Italian -- and later, English -- version is about to be published by Edizioni Terra Santa (here).
From the Middle Ages, Crusaders and pilgrims ascribed basically all majestic public works in the Holy Land to King Solomon, 10th century BC, but modern archeology provides a more complex picture.