Final answer:
The semicircular space above the doors on a Romanesque church is known as the tympanum, which is an important part of Romanesque church architecture often decorated with relief sculptures.
Step-by-step explanation:
The semicircular space above the doors on a Romanesque church is called the tympanum. This architectural element is typically decorated with sculptural relief and is found just above the church portal's lintel. The tympanum is often surrounded by archivolts (decorative arches) and serves as a focal point for narrative artwork, frequently depicting biblical scenes or imagery associated with judgment and salvation. Romanesque architecture often uses this feature to convey religious symbolism at the entrance of the church.