In architecture, a parapet is a low retaining wall at the edge of a roof, porch, or terrace.
Parapets in the Quadrangle are crenellated or battlemented - they have the distinctive pattern that frames the tops of the walls of many medievel castles, often called battlements. Crenellation most commonly took the form of multiple, regular, rectangular spaces cut out of the top of the wall to allow defenders spaces to shoot arrows from and other spaces to hide behind full cover.
Images are courtesy of the University Secretariat. Click on images for enlargement.
Above: An undecorated parapet on the former Fisher stack.
Many parapets on Quadrangle buildings are decorated with blind tracery, which refers to ornamental work of interlaced and branching lines carved on solid walls.
Above: A parapet on MacLaurin Hall decorated with blind tracery.