What is a tympanum?

A tympanum is accurately defined as a half-round panel that typically sits above the doors of a church or similar structure. This architectural feature often serves a decorative purpose, providing a space for sculptures or reliefs that can depict biblical scenes, saints, or significant iconography related to the building’s purpose. In the context of Romanesque and Gothic architecture, tympana are notable for their intricate carvings and are essential for conveying themes of spirituality and morality to the congregation.

The other options do not correctly define a tympanum. A part of the nave refers to the central part of a church building, while a decorative arch is not specific to the tympanum and can refer to various architectural features that contribute to the overall design. Thus, the half-round panel description is the most accurate representation of a tympanum.