An outwork is a minor efense, fortification, built or established outside the principal fortification limits, detached or semidetached. Outworks were developed in the 16th century, such as ravelins, lunettes (demilunes), caponiers to shield bastions and fortification curtains from direct battery. Later the increasing scale of warfare and the greater resources available to the besieger accelerated this development, and systems of outworks grew more and more elaborate and sprawling as a means of slowing the attacker's progress and making it more costly.