  thumb|upright|an extension ladder  a ladder is a vertical or inclined set of rungs or steps. there are two types: rigid ladders that can be leaned against a vertical surface such as a wall, and rope ladders that are hung from the top. the vertical members of a rigid ladder are called stringers or rails (us) or stiles (uk). rigid ladders are usually portable, but some types are permanently fixed to buildings. they are commonly made of metal, wood, or fibreglass, but they have been known to be made of tough plastic. ==variations== rigid ladders are available in many forms, such as: * assault ladder, used in siege warfare to assist in climbing walls * attic ladder, pulled down from the ceiling to allow access to an attic or loft * bridge ladder, a ladder laid horizontally to act as a passage between two points separated by a drop * cat ladder (us chicken ladder), a lightweight ladder frame used on steep roofs to prevent workers from sliding * christmas tree ladder, a type of boarding ladder for divers which has a single central rail and is open at the sides to allow the diver to climb the ladder while wearing swimfins * counterbalanced ladder, a fixed ladder with a lower sliding part. a system of counterweights is used to let the lower sliding part descend gently when released * extension ladder or "telescopic ladder", a fixed ladder divided into two or more lengths for more convenient storage; the lengths can be slid together for storage or slid apart to expand the length of the ladder; a pulley system may be fitted so that the ladder can be easily extended by an operator on the ground then locked in place using the dogs and pawls. 65 ft., 50 ft. and some 35 ft. extension ladders for fire service use "bangor poles", "tormentor poles" or "stay poles" to assist "raise, pivot, steady, extend, place, retract and lower" them due to the heavy weight. * fixed ladder, two side members joined by several rungs; affixed to structure with no moving parts * folding ladder, a ladder in the step ladder style with one or more (usually no more than three) one-way hinges. ideal for use on uneven ground (i.e. stairs), as a trestle or when fully extended a fixed ladder. some variations feature a central one-way hinge with extensible locking legs * hook ladder or pompier ladder, a rigid ladder with a hook at the t
Ladders