The Pantheon in Rome is primarily constructed from concrete and brick, with additional elements of marble and granite. The main structure of the Pantheon, including its dome, is made from concrete, a material commonly used by ancient Romans. The concrete used in the Pantheon is composed of a mixture of volcanic ash, lime, sand, and water, which provided exceptional strength and durability. While the exterior of the Pantheon is mostly concrete and brick, the interior features impressive marble columns, including sixteen monolithic granite columns with Corinthian capitals. Additionally, the Pantheon's iconic oculus, or circular opening in the center of the dome, is surrounded by a decorative ring made of Egyptian granite.