Final answer:
The column supporting the tympanum of a doorway at its center is known as a lintel, an important structural and decorative feature in Romanesque and Gothic architecture.
Step-by-step explanation:
The name of the column supporting the tympanum of a doorway at its center is a lintel. This architectural feature acts as a crossbeam that spans the space across the doorway and supports the weight of the structure above, particularly the tympanum with its decorative elements. The lintel is an essential component of the post-and-lintel construction method, which uses vertical posts or columns to support a horizontal beam.
The lintel does not only serve a structural purpose but also can be intricately carved as part of the church's decorative elements, such as sculptures and other artwork, making it an integral part of the design in Romanesque and Gothic architecture.