Final answer:
The great dome of the Pantheon is supported by Pendentives, not flying buttresses or ribbed vaults which are seen in Gothic architecture.
Step-by-step explanation:
The architectural feature that helps support the great dome of the Pantheon is C. Pendentives. Unlike Gothic architecture, which employed flying buttresses to distribute the lateral forces of high vaults and walls outwards and downwards, and ribbed vaults to support the ceiling structures of vast buildings, the Pantheon relies on its robust construction and the clever use of weight distribution inherent in its design. The Pantheon's dome, an architectural marvel, was constructed from coffered concrete without the need for any additional reinforcements such as columns or supports to hold its vast, open space. Instead, the weight of the dome is transferred down into the building's solid walls.