Several walls were discovered by Vincent (see, for example, Plates I and II in Underground Jerusalem). Their use to increase the level of water was apparently identified by M. Hecker, “Water Supply of Jerusalem in Ancient Times,” in M. Avi-Yonah, ed., Sepher Yerushalayim, Jerusalem, its natural conditions, history and development from the origins to the present day (Jerusalem, 1956), pp. 191–218 [in Hebrew]. The importance of this issue has been stressed in recent years by Abels and Arbit (see, for example, their publication cited above).