How is an obelisk defined?

An obelisk is defined as a tall four-sided structure that tapers to a point at the top. This architectural feature is commonly associated with ancient Egyptian monuments, often used to commemorate significant events or individuals. Obelisks typically stand on a square base and are made from a single piece of stone, and their design symbolizes the rays of the sun. The pointed top, known as a pyramidion, contributes to the structure's distinctive silhouette, making it a recognizable and iconic form in both ancient and contemporary contexts.

The other options describe different architectural forms that do not align with the attributes of an obelisk. For instance, a circular building would refer to structures like rotundas or pavilions, while domes, which are often found in ecclesiastical architecture, have a curved profile rather than the elongated, tapering shape of an obelisk. An open courtyard is a completely different concept, relating more to outdoor spaces within buildings rather than a defined structure.