Visigothic period (e.g. the 7th-century Church of San Juan de Baños), and to a lesser extent in Byzantine and Umayyad regions of the Middle East; however, the traditional "Moorish" arch developed into its own distinctive and slightly more sophisticated version. The mosque's architectural system of repeating double-tiered arches, with otherwise little surface decoration, is considered one of its most innovative characteristics and has been the subject of much commentary. The hypostyle hall has been variously described as resembling a "forest of columns" and having an effect similar to a "hall of mirrors". Scholar Jerrilynn Dodds has further summarized the visual effect of the hypostyle hall with the following: Interest in the mosque's interior is created, then, not by the application of a skin of decoration to a separately conceived building but by the transformation of the morphemes of the architecture itself: the arches and voussoirs. Because we share the belief that architectural components must by definition behave logically, their conversion into agents of chaos fuels a basic subversion of our expectations concerning the nature of architecture. The tensions that grow from these subverted expectations create an intellectual dialogue between building and viewer that will characterize the evolving design of the Great Mosque of Cordoba for over two hundred years. The mosque's original flat wooden ceiling was made of wooden planks and beams with carved and painted decoration. Preserved fragments of the original ceiling – some of which are now on display in the Courtyard of the Oranges – were discovered in the 19th century and have allowed modern restorers to reconstruct the ceilings of some of the western sections of the mosque according to their original style. The eastern naves of the hall (in al-Mansur's expansion), by contrast, are now covered by high Gothic vaults which were added in the 16th century by Hernan Ruiz I. On the exterior, the building has gabled roofs covered in tiles. The mihrab and the maqsura of the mosque The prayer hall also has a richly-decorated mihrab (niche symbolizing the direction of prayer) surrounded by an architecturally-defined maqsura (an area reserved for the emir or caliph during prayer), which date from the expansion of Caliph Al-Hakam II after 965. This maqsura area covers three bays along the southern qibla wall in front of the mihrab, and was marked off from the rest of the mosque by an elaborate screen of intersecting horseshoe and polylobed