Crémaillère

A Crémaillère is a French, mechanical term for the rack, or a straight bar with teeth on one edge designed to work into the teeth of a wheel or a pinion (French pignon) that predates the Renaissance. The term was generally applied in English to engineering applications which had notched, toothed or drilled surface, even when only visually so, such as the edge of the staircase. The term is also applied to the rack railway.

During the 17th to 19th centuries the term was widely applied to lines of entrenchment that are usually formed in a saw-tooth pattern, known as indented lines, particularly during sieges. These lines are usually employed on banks of rivers, or on ground which is more elevated than, or which commands, that of the enemy. The defence of these lines is sometimes strengthened by double redans, and flat bastions constructed at intervals, along their front. Just such a constructed defence was used at Centreville in 1862 during the American Civil War.

The term is also applied in Artillery to refer to an indented battery, or à Crémaillère constructed with salient and re-entering angles for obtaining an oblique, as well as a direct fire, and to afford shelter form an enfilade fire of the enemy.