Holy Spirit in the Reredos behind the High Altar of St. Peter's Basilica, Rome. Modern: Modern circular windows, which are most frequently of a simple ocular type, have an eclectic range of influences which includes abstract art, ship's portholes and the unglazed circular openings of Oriental architecture. History Origin The origin of the rose window may be found in the Roman oculus. These large circular openings let in both light and air, the best known being that at the top of the dome of the Pantheon. Windows with stone tracery make their emergence in Antiquity. Geometrical patterns of roses are very developed and common in Roman mosaic. In Early Christian and Byzantine architecture, there are examples of the use of circular oculi. They usually occur either around the drum of a dome, as at the Church of the Holy Sepulchre, Jerusalem, or high in the end of a gable of low-pitched Classical pediment form, as at Sant'Agnese fuori le mura, Rome, and Torcello Cathedral. A window of the 8th century, now in Venice, and carved from a single slab, has alternating tracery-like components of two tiers of four lancets separated by three oculi. Many semicircular windows with pierced tracery exist from the 6th to the 8th century, and later in Greece. Small circular windows such as that at S. Agnese and Torcello as well as unglazed decorative circular recesses continued to be used in churches in Italy, gaining increasing popularity in the later Romanesque period. The German art historian Otto von Simson considered that the origin of the rose window lay in a window with the six-lobed rosettes and octagon which adorned the external wall of the Umayyad palace Khirbat al-Mafjar built in Jordan between 740 and 750 CE. This theory suggests that crusaders brought the design of this attractive window to Europe, introducing it to churches. But the decorative pattern for rose and, independently, the tracery, are very present in vestiges of the early Christian architecture, Byzantine architecture, and especially in Merovingian art, and Visigothic architecture before the Muslim conquest of Spain. But also half roses are known, as with the church of San Juan Bautista in Baños de Cerrato. The scarcity and the brittleness of the vestiges of this time does not make it possible to say that complete rose window in tracery did not exist in early Middle Ages. The windows of Oviedo In the vicinity of