A balustrade is an architectural railing system consisting of a top rail, supporting vertical posts (called balusters), and often a base rail. In castles, they serve a dual purpose: providing fall protection along elevated edges (like battlements or parapets) and adding ornate decoration to the structure's exterior and interior spaces.

A complete balustrade system consists of the following interconnected parts:
Balusters: The individual (often bulbous or vase-shaped) vertical posts, pillars, or spindles that support the weight of the railing.

Handrail (Top Rail): The horizontal beam that connects the tops of all balusters, acting as both a primary touchpoint and a structural binder.

Base Rail: The lower horizontal rail that holds the bottoms of the balusters securely in place and evenly distributes weight.

Newel Posts: Larger, heavy structural posts placed at the corners or ends of a balustrade run to provide critical stability.

Functionality in a Castle:
Parapet & Roofline Protection: While medieval castle roofs were heavily crenelated (notched) for archers to fire through, later Renaissance and Gothic revival castles utilized balustrades to enclose flat roofs, terraces, and open-air galleries.

Courtyard Aesthetics: Castle balustrades were frequently carved from stone (like marble or granite) or cast from decorative metals. They lined interior courtyards, grand staircases, and second-floor walkways to showcase wealth and architectural grandeur.

Safety & Division: Primarily, they cordoned off exposed drops or separated private rooms from grand communal spaces without blocking natural light or visibility.