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How does the oculus of the Pantheon light the building?
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Hadrian
White marble statue of the Roman emperor Hadrian, from an excavation at Sagalassos in southwest Turkey.
The Pantheon, rebuilt by the emperor Hadrian between 118 and 128 CE, is an architectural marvel designed to favor its interior space. The building is lit solely by the oculus—a 27-foot (8-meter) circular opening located at the center of its massive concrete dome.123
This "great eye" serves as the structure's only source of natural light. As sunlight streams through the opening, it floods the rotunda, illuminating the interior's polished marble surfaces and coffered ceiling geometry. The effect is particularly striking around noon, when the light sets the space aglow. Because the oculus is open to the elements, the building features a sloping floor specifically designed to drain away any rainwater that enters through the aperture.21