Final answer:
The corbel arch is the oldest known type of arch, preceding even the round arch from Mesopotamia. It was used by the Mycenaeans for supporting heavy structures above doorways.
Step-by-step explanation:
The oldest known type of arch is the corbel arch. This arch was utilized by ancient civilizations, such as the Mycenaeans, to create supportive structures in their architecture.
Constructed by offsetting successive courses of stone or brick at the springline of the walls, the corbel arch projects towards the archway's center from each supporting side until the courses meet at the apex, often with a flat stone bridging the last gap.
This method relieved weight on the lintels above doorways, providing the necessary support for the heavy structures built on top of these arches.
While the round arch is often attributed to the Romans, it was actually the Mesopotamians who first originated this structural system, which allowed for larger openings and improved airflow in load-bearing walls. However, it is the corbel arch that predates the round arch and thus is considered the oldest known type in historical architecture.