Which structure is described as an obelisk?

An obelisk is specifically defined as a tall, four-sided pillar that tapers to a pointed top. This distinct geometric shape is often associated with ancient Egyptian architecture, where obelisks served both a commemorative purpose and a symbolic one, representing the sun’s rays. The tall and narrow form of an obelisk creates a striking visual presence, often seen in public spaces and monuments to honor significant historical figures or events.

The other options describe different architectural features that do not fit the characteristics of an obelisk. A large rectangular building does not have the pronounced verticality or tapering shape, a decorative fountain typically encompasses flowing water and design elements that do not align with the simplicity of an obelisk, and a circular architectural feature lacks the distinct pointed top that is essential to the definition of an obelisk. Thus, the description that captures the essence of what an obelisk is, is indeed the tall, four-sided pillar that is pointed at the top.