In the arms of the transept are fine columns of granite, verd antique, travertine, and lumachello[339], supporting capitals of different patterns and unquestionable antiquity. In the western arm, on the left hand, are two columns of verd antique, a small distance apart, called by the Mohammedans the 'Columns of Proof,' because, according to our guide, all who enjoy the favour of God can pass through the narrow space between them, but not those who are wicked. The worn state of their inner sides shews the great number of the faithful who have passed the test. This arm terminates in a long hall, whose low vaulted roof is supported by pointed arches springing from many-sided pillars; it is called the mosque of Abu-Bekr, but is really an ancient gallery built by the Crusaders. Our guide tells us that in their time it was used as an armoury, which is doubtless the truth, as the mosque _el-Aksa_ itself was converted into a dwelling-house. At the end of the eastern arm is a small vaulted hall, resting on the city wall and lighted by windows commanding a fine view of the slopes of Ophel, part of the Kidron valley, and the Mount of Offence with the village of Siloam. This chamber is supposed to be the place in which Omar prayed for the first time within the walls of the _Haram_: by the spot where he knelt there is a niche, ornamented with two columns of clouded grey marble, which have been inverted by the architect, so that the capitals richly carved with leaves serve as bases. This is called especially the mosque of Omar, as it continued to be the private oratory of the Khalif. On turning back to enter the main building, we see on the right a kind of chapel, wherein is a niche ornamented with marble, called _Bâb er-Rahma_ (Gate of Mercy), near it are the _Mikhereb_ of S. John (Baptist) and Zacharias. On quitting the mosque by the great northern door, and turning to the right, we find a flight of steps leading down to the subterranean vaults below it.