Page "Siege" Paragraph 27

Disease was another effective siege weapon, although the attackers were often as vulnerable as the defenders.

In some instances, catapults or similar weapons were used to fling diseased animals over city walls in an early example of biological warfare.

If all else failed, a besieger could claim the booty of his conquest undamaged, and retain his men and equipment intact, for the price of a well-placed bribe to a disgruntled gate-keeper.