The plain black flag, being the opposite of the plain white flag of peaceful surrender, represents no surrender by patriotic forces and no quarter given to enemies. In times past it was not uncommon for enemy combatants who surrendered to be free to pass into friendly territory or to defect after an oath to give up their fight, feeding and housing a large number of prisoners was costly. Those taken prisoner could often expect to be later pardoned or exchanged, especially if they were officers or well off. When the black flag was flown it was an unmistakable symbol that no prisoners would be taken and captured enemy combatants would be killed. When surrender terms were presented a black flag meant there would be no surrender, those fighting knew they would be killed and vowed to fight until death.