What structural element spans the top of the fireplace opening and supports the face of the fireplace?

The lintel is the structural element that spans the top of the fireplace opening and provides support for the weight of the materials above it, such as the chimney, mantel, or masonry. This is crucial in maintaining the integrity of the fireplace structure. Lintels are typically made from materials such as wood, steel, or stone and are designed to bear the load without bending or cracking.

In contrast, a header is generally used in framing, often above doors and windows, and serves a similar purpose but is not specifically designed for fireplaces. The architrave refers to the decorative molding that frames the fireplace and does not provide structural support. A beam is a broader term for a structural element that supports loads but is not specifically tailored to the unique needs of a fireplace opening like a lintel is. Thus, the lintel is the correct answer as it specifically addresses the support needs above a fireplace.