A parapet is a barrier that is an upward extension of a wall at the edge of a roof, terrace, balcony, walkway or other structure. The word comes ultimately from the Italian parapetto. Where extending above a roof, a parapet may simply be the portion of an exterior wall that continues above the edge line of the roof surface, or may be a continuation of a vertical feature beneath the roof such as a fire wall or party wall. Parapets were originally used to defend buildings from military attack, but today they are primarily used as guard rails, to conceal rooftop equipment, reduce wind loads on the roof, and to prevent the spread of fires.
The crenellated parapet on a bastion of Kyrenia Castle, Cyprus
A modern, transparent parapet surrounds a New York City rooftop.
Elaborate parapets flank the roof of King's College Chapel, Cambridge.
A modern parapet with integrated lighting functions as a guard rail along the BP Pedestrian Bridge in Chicago
Guard rails, guardrails, railings or protective guarding, in general, are a boundary feature and may be a means to prevent or deter access to dangerous or off-limits areas while allowing light and visibility in a greater way than a fence. Common shapes are flat, rounded edge, and tubular in horizontal railings, whereas tetraform spear-headed or ball-finialled are most common in vertical railings around homes. Park and garden railings commonly in metalworking feature swirls, leaves, plate metal areas and/or motifs particularly on and beside gates.
Staircase railings in the Degré du roi, part of the Petit appartement du roi, in the Palace of Versailles, Versailles, France
Sign in Niagara Falls, Ontario, warning people not to climb over guard rail overlooking the Niagara River
A handrail leading along a rocky creek crossing
A crowd barrier (guard rail — North America) collapses at a college football game, spilling fans onto the sidelines.