of early Islamic architecture. The earliest mosques before this had been relatively plain hypostyle structures (a flat-roof hall supported by columns), but the new mosque in Damascus introduced a more basilical plan with three parallel aisles and a perpendicular central nave. The central nave, which leads from the main entrance to the mihrab (niche in the qibla wall) and features a central dome, provided a new aesthetic focus which may have been designed to emphasize the area originally reserved for the caliph during prayers, near the mihrab. There is some uncertainty as to whether the dome was originally directly in front of the mihrab (as in many later mosques) or in its current position mid-way along the central nave. Scholars have attributed the design of the mosque's plan to the influences of Byzantine Christian basilicas in the region. Rafi Grafman and Myriam Rosen-Ayalon have argued that the first Umayyad Al-Aqsa Mosque built in Jerusalem, begun by Abd al-Malik (al-Walid's father) and now replaced by later constructions, had a layout very similar to the current Umayyad Mosque in Damascus and that it probably served as a model for the latter. The mosque initially had no minaret towers, as this feature of mosque architecture was not established until later. However, at least two of the corners of the mosque's outer wall had short towers, platforms, or roof shelters which were used by the muezzin to issue the call to prayer (adhān), constituting a type of proto-minaret. These features were referred to as a mi'd͟hana ("place of the adhān") or as a ṣawma῾a ("monk's cell", due to their small size) in historical Arabic sources. Arabic sources indicated that they were former Roman towers which already stood at the corners of the temenos before the mosque's construction and were simply left intact and reused after construction. Decoration The mosque was richly decorated. A rich composition of marble paneling covered the lower walls, though only minor examples of the original marbles have survived today near the east gate. The walls of the prayer hall were raised above the level of the old temenos walls, which allowed for new windows to be inserted in the upper walls. The windows had ornately carved grilles that foreshadowed the styles of windows in later Islamic architecture. The most celebrated decorative element of all was the revetment of mosaics, which originally covered much of the courtyard and the interior hall.