"From this central block rose the twin towers, ancient, crenelated, and pierced with many loopholes."
Battlement - Wikipedia, the free encyclopedia: "A battlement (also called a
crenellation) in defensive architecture, such as that of city walls or castles, comprises a parapet (i.e. a short wall), in which portions have been cut out at intervals to allow the discharge of arrows or other missiles. These cut-out portions form crenels (also known as carnels, embrasures, loops or wheelers)."
Image via Wikipedia