On a recent visit to Italy, your friend Gina admired the famous Pantheon in Rome. It was built using an architectural feature that resembles the upper half of a sphere or circle. It also allowed for the construction of vaulted ceilings without having to use crossbeams. What is the structure Gina observed that is so crucial to the construction of the Pantheon? (1 point)
dome
barrel vault
flying buttress
arch