In architecture, circular openings have been held with very high fascination. A circle is a centric and balanced shape and so fits into any composition. Oculus is a Latin term meaning an eye (Oculi -plural). In architecture, oculus has become synonymous with the pair of volutes on Ionic column and the Roman circular gaps or openings.
The purpose of many such circular openings was mostly architectural composition, and sometimes to allow subtle light to illuminate the interior spaces rather to see the exterior. The circular gaps were often completely open, with pierced panels or glazed with crude glass -as was available at the time.
Oculi openings are also called: Oeil-de-boeuf, Bull’s-eye, Ox-eye, Wheel, or Roundel windows. Oculi is small circular or oval shaped gap in the upper sections of the walls, over doors and other openings, cupolas, in roofs, on the drums that support the dome, in the ends of a gable roof, or within a pediment over an opening system. These are also placed on the top of a dome as in Roman Pantheon.
Circular openings have originated from the Roman circular gaps or oculus. Circular windows and decorative circular recesses are a feature of many Romanesque churches and cathedrals, such as in Santa Maria in Pomposa, Italy, 10th C. However, it was by the middle of the 12th C that it became larger in size and a richly decorated element. By the middle of the 13th C its size had increased to cover the entire width of the nave. Circular windows were placed mainly at the West end of the nave and the ends of the transepts.
OEIL-DE-BOEUF WINDOW: In French, oeil-de-boeuf means ‘eye of the steer’. It is a small circular window resembling a wheel, often with radiating glazing bars similar to spokes of a wheel.
WHEEL WINDOW: Wheel window is a circular window divided by simple spokes radiating from a central boss or opening.
ROSE WINDOW: Rose window is also a circular window wherein the straight spokes became rounded at the outer edge, and at the centre began from a hollow roundel. The Rose window has more complex design that looks like a multi-petalled rose. The term Rose window is often used as a generic term applied to any circular window. The term Rose window is especially used for those found in churches of the Gothic architecture. The Gothic Rose window is divided into segments by stone mullions and tracery. The name Rose window was not used before the 17th C. A simple circular window without tracery is called an ocular window or oculus.
Rose windows with pierced openings rather than tracery occurred in periods between the Romanesque and Gothic. Many varied patterns evolved across Europe. Rose windows were initially placed under round arch, but later began to be accommodated within a pointed arch, as was done in the Reims Cathedral 1230. Rose windows have been inscribed in square, with pierced spandrels, as in Notre Dame of Paris, 1257.
German art historian Otto Von Simson considers the origin of the rose window to the six lobed rosettes and octagon windows which adorned the external wall of the Umayyad palace Khirbat al-Mafjar built in Jordan around 740. The theory suggests that crusaders brought the design of this attractive window to Europe, introducing it to churches.
In Baroque period many shapes of ocular windows were used. These were oval or of a more complex shape. They were of very simple form, neither traceried nor crossed by mullions, but were mounted by ornate carving. The Baroque oculi were rarely a dominant visual element, either over the façade or on the interior face. Compared to this the great Gothic windows, were very important elements of the façade scheme.
Modern circular openings include L Khan’s Indian Management Institute, Ahmedabad and Assembly buildings at Dhaka, Bangladesh. Other examples include modernistic circular openings, marine and space ships’ hatch windows.