Which of the following architectural features is primarily decorative and supports the structure?

The correct answer is the balustrade, which serves as a railing or barrier supported by a series of posts or balusters. While its primary function is to provide safety and support, a balustrade is also often elaborately designed, making it a decorative architectural feature. Its aesthetic value can enhance the visual appeal of staircases, balconies, and other elevated areas while still maintaining the structural integrity of those spaces.

The facade primarily refers to the front or face of a building, which may involve intricate designs and is more about the overall appearance rather than a specific structural supportive element. The spire is a tall, tapering structure on top of a building, often decorative, but it does not significantly contribute to the structural support of the building itself. Gargoyles, while they may have a functional aspect in directing water away from a building, are primarily known for their ornamental characteristics. Thus, they serve more as decorative elements than as structural supports.