The Western Wall Tunnel. The most striking portion of the wall, about 60 feet north of Wilson’s Arch, appears above. Dubbed the “Master Course,” it consists of four blocks 11 feet high. They vary from 6 feet long to a staggering 42 feet, the latter estimated to be 14 feet deep and weighing 1,200,000 pounds! The square holes probably date to the second century C.E. and were part of the Roman transformation of this area into a plastered cistern. Stone pegs inserted into these holes held a rough stone facing that then received a waterproof plaster coating. Though the area on the other (eastern) side of the Master Course cannot be explored (it lies under the Temple Mount itself, on which the Dome of the Rock sits), radar soundings have revealed a huge vaulted area there, which may have served as a vast storeroom for the Temple and its priests. The Master Course probably served as a support and counterforce to the open vault on its other side.