Which Roman structure features a large concrete dome with a central opening?

The Pantheon is renowned for its impressive architecture, particularly its large concrete dome, which remains one of the largest unreinforced concrete domes in the world. The dome is a significant architectural achievement of ancient Rome and is approximately 43.3 meters in diameter, showcasing the Romans' advanced engineering skills.

At the apex of the dome is the oculus, a central opening that allows natural light to illuminate the interior and serves as a symbolic connection to the heavens. This design not only enhances the aesthetic appeal of the structure but also serves practical purposes, such as ventilation and reducing the weight of the dome.

The Pantheon's architectural innovations, including its harmonious proportions and the way the dome transitions smoothly from a circular shape to a square base, exemplify the ingenuity of Roman builders and their ability to create enduring structures that have influenced architecture throughout history.

In contrast, the other structures listed have different functions and architectural styles that do not feature such a prominent dome with an oculus. The Colosseum is known for its amphitheater design; the Forum served as a public space for political, legal, and social activities; and aqueducts were constructed for transporting water.