By the mid-eighteenth century, military engineers had developed principles for constructing forts, from the number of men needed to defend each bastion—a thousand or so—to the number of cannons per bastion—a dozen or so—to the need for cavalry sorties and water cisterns. For a typical six-week siege, a hundred tons of powder might be required. When hard-pressed by attackers, a recent British field manual advised, “engines may be contrived to fling heavy stones … or to blow dust or sand in their faces,” much as besieged Tyre had flung heated sand at Alexander’s shock troops, or Hannibal in a
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