According to geologist Dan Gill, who served as geological consultant to Yigal Shiloh’s excavations in the City of David, in cutting the tunnels, the diggers followed the lines of a natural system of underground channels, caverns and shafts. This required significantly less cutting, but meant they had to cover more ground: A straight tunnel from the entryway to the top of Warren’s Shaft would be only 82 feet; their tunnel extends 136 feet. (See Dan Gill, “How They Met: Geology Solves Long-Standing Mystery of Hezekiah’s Tunnelers,” BAR 20:04.)

Gill’s explanation is not accepted by author Ronny Reich, who suggests that although the system does include natural (karstic) elements such as the shaft, these features are neither interconnected nor continuous, and therefore could not have determined the plan of the entire tunnel system. According to Reich, the long arm of the horizontal tunnel is best explained by the need for a gradually inclining tunnel. A tunnel leading straight from the system entrance to the shaft would simply have been too steep.