[Illustration: The Mechanics of a Siege
Military engineers built forts for several reasons: to protect cities,
to protect strong points from falling into enemy hands, to be a visible
symbol of governmental authority. If a fort could not be taken by
surprise, an attacking party had to take the fort by force. The process
of surrounding an enemy’s strong point and slowly cutting off all
contact with the outside world is known as a siege. Sieges go back to
Biblical times, but the principles were formulated by Sébastien le
Prestre de Vauban (1633-1707), a French military engineer who served in
the armies of Louis XIV. He created a very formal, disciplined science,
and his plan was maddeningly simple. First a trench parallel to the fort
was dug out of gun range so the attackers could move in supplies and
troops. Sappers—crews of trench diggers—then dug zigzag trenches toward
the fort; the zigzag pattern made it more difficult for defenders to hit
the trenches. Next the sappers dug a second parallel that included some
batteries for shelling the fort. Additional zigzag trenches and
parallels would be dug until the attackers were in a position to
concentrate their fire at one point on the fortification to breach its
walls. The fortress would then have no alternative but to surrender or
be stormed. Conducting a textbook perfect siege did not always result in
success, for the fort’s defenders would not have been idle. They would
fire cannon at the sappers. Often they dug counter trenches out from the
fortress and planted mines to blow up the work of the attackers. And
they would send out nighttime raiding parties, too.