A parapet is a barrier at the edge of a roof or balcony which is designed to provide protection to the structure and to people behind the parapet. The term "parapet" was also used in trench warfare, to describe the fortifications at the top of a trench designed to protect occupants from enemy fire and to provide cover for assaults on the enemy. Parapets are a feature of design in many cultures, and some very fine examples can be seen around the world, serving decorative, defensive, and safety functions.
Classically, a parapet is made from masonry. It may be an extension of an underlying wall, or a separate construction, depending on the design. Parapets are usually high enough that they can prevent someone from falling, and some may be so tall that people are entirely concealed behind them. High parapets are a hallmark of defensive architecture, providing cover to defenders situated on roofs and balconies. Lower parapets are more ornamental and safety oriented.
In the case of a plain parapet, the parapet is solid. Perforated and embattled versions are pierced. The openings created could be used historically by defensive forces to attack the enemy without exposing themselves to risk; arrows could be fired through the holes, for example. Today, pierced parapets serve a more decorative function, looking more visually interesting than solid plain designs.
Beyond defense, parapets can also be useful for building safety. They keep people from falling, and they can limit the spread of a fire. Some fire walls extend up over the edge of the roof in the form of parapets, limiting the spread of fire from roof to roof. Parapets are also used ornamentally, to conceal the specifics of a roof if an architect feels that a roof is not visually interesting or does not fit well with the aesthetics of the rest of a structure.
Many architects take advantage of their parapets to add some decorative flair to their buildings. The exterior can be decorated with carvings and other designs, and the top of the parapet can be made interesting by changes in level which create a pattern. With pierced parapets, openings of various shapes and sizes can be created to add visual interest to the appearance of the parapet, or to provide cutaway glimpses of the structure behind the parapet. More stylized versions can look more like railings than parapets, with a very minimalist design.