The Umayyad mosque at Damascus is also abnormal, but its plan seems to have been far more directly determined than in the Aqṣâ by the building which preceded it on the same site. The nave and aisles of the church of St. John must have dictated the scheme of its arcades, and its distinguishing feature, the wide central aisle running north and south, can only be explained by a similar disposition, either transept or narthex, in the church.[408] It is conceivable that the temple porticoes may have given the impulse to the full development of the riwâqs about the ṣaḥn, just as the porticoes of such buildings as the Serapeion, the agora, and the gymnasium at Alexandria, or of the stoas and agoras which adorned the Hellenistic cities of the Roman empire, may have had their share in suggesting an extension of the colonnades of the mosque, and indeed in Mesopotamia, where these models were absent, there is no reason for supposing that the riwâqs were carried in the first constructions all round the ṣaḥn. But this extension was in itself a not unnatural growth out of the Medînah plan, and in its further history, the courtyard-mosque with its deep ḥaram and its narrow flanking riwâqs pursued its own line of development, based upon its own needs. In this development no doubt the renowned Umayyad mosque at Damascus played a part. In Syria both the Aqṣâ and the mosque at Ba’albek show the wide central aisle running north and south.[409] It is typical of the Tunisian mosques, but here it is almost always found in conjunction with a wide transept running parallel with the qiblah wall; a dome covers the miḥrâb where the wide aisle and the transept meet, and a second dome stands at the opposite end of the central aisle. This =⏊=-shaped scheme can be seen at Qairawân, in the Zaitûnah at Tunis, at Tilimsân, and elsewhere. The mosque of Qairawân was founded in A.D. 671, but entirely rebuilt, first in 703 and again in 837.[410] The Zaitûnah was founded in A.D. 732. The great mosque at Cordova, founded at the end of the eighth century, had the same disposition.[411] The Tilimsân mosques are considerably later in date and are built with piers, with the exception of Sidi al-Ḥalwi, where both piers and columns are used.[412]