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Hezekiah’s Tunnel, which is visited often by tourists including many Christadelphians, is the longest tunnel ever built without intermediate man-made shafts at the time of its completion. It is more than 1,700 feet long (just about 1/3 of a mile). Any way one looks at it, Hezekiah’s project is an extraordinary feat of construction, requiring engineers to create a tunnel going from one side of Jerusalemto the other. It starts at the Gihon Spring, Jerusalem’s only natural source of water, and curves around to the Siloam Pool on the other side of the City of David [see the map below].

Hezekiah built the tunnel in anticipation of a threatened siege of the city by the Assyrian ruler Sennacherib. The Gihon Spring lay outside the eastern city wall, near the floor of the Kidron Valley. In peacetime, Jerusalemites walked a few feet outside the city to get their water, something they could not easily do when the city came under siege. The tunnel rendered this concern moot when water became available inside the city.

The Bible describes Sennacherib’s tactics quite dramatically. His messengers, though ostensibly sent to threaten Hezekiah directly, spoke openly to the people on the walls ofJerusalem. Hezekiah’s representatives asked Sennacherib’s men to speak in Aramaic (the diplomatic language of the day) instead of Hebrew so the people would not understand:

“Please, speak to your servants in Aramaic, for we understand it; do not speak to us in Judean in the hearing of the people on the wall” (2Kgs18:26).

Sennacherib’s envoys replied that it was precisely to the people on the wall that they wanted to speak.

So, among other preparations, Hezekiah built a tunnel to bring water into the soon-to-be-besieged city:

“When Hezekiah saw that Sennacherib had come, intent on making war on Jerusalem, he consulted with his officials and military staff about blocking off the water from the springs outside the city… It was Hezekiah who blocked the upper outlet of the Gihon spring and channeled the water down to the west side of the City of David” (2Chron 32:2,3,30; cp 2Kgs 20:20).

Whether because of the tunnel or a miracle (see 2 Kgs 19:35), Sennacherib’s siege was unsuccessful. Even he admitted this in what has become a famous cuneiform inscription, where the Assyrian monarch brags that he had Hezekiah cornered in Jerusalem“like a bird in a cage”. However this is in direct contrast to other Assyrian conquests in which the king’s triumphs were laid out in shameless self-promotion. Quite in contrast, with Jerusalem, Sennacherib made no claim of capturing the “bird” or conquering the city, and seems content to put his stalemate in the best possible light.

The tunnel mystery

The construction of the tunnel has always been something of a mystery. Ever since Hezekiah’s Tunnel was discovered in the mid-19th century by the American explorer Edward Robinson, scholars have puzzled over how the two teams of tunnelers met. While digging from opposite ends of the city, and even considering an especially winding route, they still managed to meet in the middle.

We know that it was dug by two teams digging from opposite ends due to the famous Siloam Inscription that was carved in the tunnel wall and discovered in 1880. Describing how the two teams of tunnelers met, the inscription reads:

“This is the account of the breakthrough. While the laborers were still working with their picks, each toward the other, and while there were still three cubits to be broken through, the voice of each was heard [through the rock] calling to the other, because there was a zdh [split? crack? overlap? resonance?] in the rock to the south and to the north. And at the moment of the breakthrough, the laborers struck each toward the other, pick against pick. Then the water flowed from the spring to the pool for 1,200 cubits. And the height of the rock above the heads of the laborers was 100 cubits.”

If they were so smart, some ask, why didn’t they take a more direct route? A straight line would have produced a tunnel of about 1,050 feet. The route they took was 1,748 feet, about 700 extra feet, or 70% longer than necessary if it had been dug in a straight line.

What “trail”did they follow?

Between 1978 and 1982, Yigal Shiloh directed a major excavation of the City of David and its water systems. His staff included a geologist named Dan Gill from the Geological Survey of Israel who studied Hezekiah’s Tunnel. In the end, Gill adopted and expanded an explanation put forward as early as 1929 by an English architect named Henry Sulley, of some Christadelphian notoriety (Quarterly Statement of Palestine Exploration Fund, 1929, p. 124). This suggested explanation was that a small natural tunnel or stream preceded and guided the engineers who dug Hezekiah’s Tunnel. They simply enlarged what had been there before. Gill expanded this explanation with a study of the geology of the site. According to Gill’s 1994 BAR article, Hezekiah’s Tunnel was “fashioned essentially by skillful human enlargement of natural (karstic) dissolution channels”. These natural tunnels, or karstic dissolution channels, form by acidic waters percolating through the rock, which occurs where the water has easy access through the rock — that is, along fractures and joints. This widens the cracks, forming subterranean tunnels, chimneys and caves that could be followed by tunnelers quite easily.

A new study by Aryeh Shimron and Amos Frumkin, however, now proves this theory wrong and goes on to explain how the two teams of tunnelers really found each other.

One of the serious objections to the karstic-dissolution-channel theory is simply the meeting point of the tunnelers. On either side of the point where the tunnels collide, there are several twists and turns in various directions that start about a hundred feet from the meeting point. Just as you can read in the Siloam Inscription, these abortive tunnels seem to show the efforts of each group to find the other.

Gill addresses these false tunnels by suggesting that the original water channels may have forked at these points and the tunnelers took the wrong fork, only to quickly discover their mistake. Alternatively, he also suggested that the false tunnels may have been intentionally created to allow two-way traffic for maintenance personnel who would periodically clean the channel of debris.

While possible in a theoretical sense, these explanations seem a bit of a stretch. If the tunnelers really had been following a dissolution channel created by flowing water, why did they have so much trouble finding each other when they were only a hundred feet apart? Why would these side channels all coincidentally occur on both sides of the tunnel at the exact spot of the meeting, while not occurring elsewhere? Would the proposed maintenance tunnels only have been necessary at the point of meeting and nowhere else?

Shimron and Frumkin’s article adds scientific weight to these logical, but not totally provable, objections. Shimron mapped the direction of hundreds of geological joints and fractures that cut across the ceiling and walls of the tunnel and came to a simple conclusion. Karstic voids should form parallel along a single fissure, or a group of such fissures. Therefore, Hezekiah’s tunnel cannot originally have been following a karstic-formed geological feature because it runs effectively perpendicular to these natural tunnels.

Shimron also studied the plasters and natural sedimentary deposits in the tunnel. There were four different kinds of plaster in the tunnel. The oldest plaster was succeeded by Byzantine plaster, next by a Mameluke-period plaster, and finally by a plaster applied in the early 20th century. Sedimentary deposits laid down from running water (tufa) and water seeping through tunnel walls (flowstone, a kind of stalactite attached to tunnel walls) also occur along various segments of the tunnel. Patches of the oldest plaster were preserved beneath flowstone, which turned out to be a critical finding.

Cores that were collected along the length of the tunnel floor revealed that tufa and siltstone covered all the plaster layers but were never found beneath the oldest plaster. This demonstrated that there was no percolating water and, most likely, no original channel that was widened by Hezekiah’s tunnelers. Had there been a karstic channel which served as a guide, sediments (such as those that covered the plaster) would have been deposited from the running water and would have been found beneath even the oldest plaster. The absence of these sedimentary deposits also shows that the ancient plaster was applied soon after the tunnel was dug, before the natural sedimentation process caused by the flow of water through the tunnel could begin.

You might ask, “What if the stream along the karstic tunnel was only a trickle? What if the drill cores missed this narrow stream? What if tunnel construction removed all trace of the original channel?” The new study has an answer: Frumkin examined more than a thousand karstic cave passages in and around Jerusalem. He found that the cross-section of these passages is, on average, larger than the width of Hezekiah’s Tunnel. Based on these studies, Shimron and Frumkin conclude that “total obliteration of a [karstic] conduit by the narrow Siloam Tunnel is virtually impossible.”

The teams meet

But the question that started all this speculation and scientific research remains unanswered: How did the two teams of tunnelers manage to meet after wandering around so widely? Shimron and Frumkin suggest that the tunnelers were guided by communications from the surface; specifically by hammering on the bedrock. Experiments conducted by Shimron and Frumkin showed that tapping with a hammer on the bedrock above the tunnel was effective up to 50 feet below the surface and could still be detected up to 80 feet. In short, “Acoustic messages between tunnel and surface must have been the dominant technique which controlled the complex proceeding underneath.” (Acoustic communication has been used for centuries as the method for locating people trapped in mines and earthquake collapses.)

Shimron and Frumkin found the shift in direction taken by the two teams of tunnelers somewhat puzzling. Apparently, the final course of the tunnel was not constructed as initially planned by Hezekiah’s engineers. The section that started on the northern end of the city shifts from a generally western direction to a southern one, while the southern portion of the tunnel moves from a generally eastward to a northern one. Shimron and Frumkin speculate that when the tunnelers got to the middle of the hill and found themselves beneath some 160 feet of stone, they realized that they were well beyond the range of sound communication. It would have become clear to the engineers that a meeting of the two teams would become difficult, if not impossible, under these conditions. The two authors theorize that a decision must have been made to change the course of each segment and shift the direction to where the depth of stone is shallow and where surface-to-underground communication would be feasible.

In light of the information presented by Shimron and Frumkin, the final piece of the puzzle of how the tunnel was constructed might be found simply by rereading the Siloam Inscription. If, as has been suggested, Hezekiah’s engineers used acoustic sounding to guide the tunnelers then the frequently ignored final sentence of the inscription provides a final bit of evidence: “And the height of the rock above the heads of the laborers was 100 cubits.” In light of the idea of acoustic sounding, this last sentence indicates that the engineers were well aware of the height of the rock above the tunnel at various points in its progression. And it could explain the last few abortive attempts by the tunnelers to find each other. Confused by the sounds of the other miners and lack of easy communication with the surface (since 100 cubits is well beyond the easy range of acoustic sounding), it took the tunnelers a few attempts to find each other. But when they did, we have the final few lines of the inscription to describe the event: “And at the moment of the breakthrough, the laborers struck each toward the other, pick against pick. Then the water flowed from the spring to the pool for 1,200 cubits.”

Adam Booker

It is suggested that the original intent of the two teams of tunnelers was to go from Point 4 to Point 7, and from Point 7 to Point 4, respectively. Here’s what may have happened:

1. The north team, starting from the Gihon Spring, heads west in a slightly downhill grade (while the land surface rises above it).
2. The south team, starting from the Siloam Pool, crosses east under the peak of the City of David, hoping to run northward on the east side of the ridge.
3. The north team loses acoustic sound from above, and decides to alter course and head south.
4. Likewise, the south team, intending to head north, realizes they will lose acoustic sound like the north team has. So they decide to change course, to the southeast, until they can hear the overhead tapping again.
5. The north team intends to head due south.
6. The south team is redirected toward the north to meet the other team.
7. The north team makes a slight course correction because of the location of the south team.
8. At this point, the north team can be heard again by acoustic sounding.
9. Both teams must make final adjustments, based on their own underground acoustic sounding, so as to intersect.