(Latin: “eye”) In architecture, any of several elements resembling an eye, such as a round or oval window or the round opening at the top of some domes (see Pantheon). The capital of an Ionic column features an oculus in the form of a disk at the centre of each of its spiral scrolls.
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Oculus (plural oculi) is the Latin word for eye, and the word remains in use in certain contexts, as the name of the round opening in the top of the dome of the Pantheon in Rome, and in reference to other round windows and openings.
The Oculus in the Pantheon has always been open to the weather, allowing rain to enter and fall to the floor, whence it is carried away through drains. In the picture, right, sunlight streams through the opening and strikes the lower part of the dome. The bright opening and the surrounding smooth concrete above the coffering resembles an eye, giving the opening its name.
Circular windows, a feature of Classical architecture since the sixteenth century are often denoted by their French name, oeil de boeuf, or "bull's-eye". Such circular or oval windows express the presence of a mezzanine on a building's façade without competing for attention with the major fenestration. Circular windows set in dormers have been a feature of French Classical architecture since the beginning of the seventeenth century. For structural reasons, they are also found as the portholes of ships. In archaeology, oculus is the name given a motif found in western European prehistoric art. It consists of a pair of circular or spiral marks, often interpreted as eyes, and appears on pottery, statues and megaliths. It may represent the watchful gaze of a god or goddess (see dolmen deity for example) and was especially common during the Neolithic period.