Parapet

A parapet is a barrier which is an extension of the wall at the edge of a roof, terrace, balcony, walkway or other structure. The word comes ultimately from the Italian parapetto (parare "to cover/defend" and petto "breast"). The German equivalent Brustwehr has the same meaning. Where extending above a roof, a parapet may simply be the portion of an exterior wall that continues above the 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 and to prevent the spread of fires.

Parapets may be plain, embattled, perforated or panelled, which are not mutually exclusive terms.

The Mosaic law prescribed parapets for newly constructed houses as a safety measure (Deuteronomy 22:8).

The Mirror Wall at Sigiriya, Sri Lanka built between 477 and 495 AD is one of the few surviving protective parapet walls from antiquity. Built onto the side of Sigiriya Rock it ran for a distance of approximately 250 meters and provided protection from inclement weather. Only about one hundred meters of this wall exists today, but brick debris and grooves on the rock face along the western side of the rock clearly show where the rest of this wall once stood.

Parapets surrounding roofs are common in London. This dates from the Building Act of 1707 which banned projecting wooden eaves in the cities of Westminster and London as a fire risk. Instead an 18-inch brick parapet was required, with the roof set behind. This was continued in many Georgian houses, as it gave the appearance of a flat roof which accorded with the desire for classical proportions.

...
Wikipedia