Engines of Our Ingenuity

No. 664:

by John H. Lienhard

Click here for audio of Episode 664.

Today, King Hezekiah is a better engineer than we thought. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

King David captured Jerusalem in 1000 BC. That's why Jerusalem is called "The City of David." But there's something very odd about the way he did it. He called on a volunteer to lead a group into the city through some kind of underground tunnel. In the the Second Book of Samuel, David says,

Whosoever getteth up to the gutter, and smiteth the Jebusites ... he shall be chief and captain.

It's that word gutter, or maybe it should be water pipe, that we wonder about. You see, Jerusalem gets its water from a source called Gihon Spring -- even today. Gihon Spring lies outside the city and below it.

But there wasn't any tunnel for water in 1000 BC. Three hundred years later, in 701 BC, King Hezekiah cut a tunnel down to the Spring. He dug it to supply water during an Assyrian siege. It says in 2nd Kings: "[Hezekiah] made a pool, and conduit, and brought water into the city"

So how did David's man get into Jerusalem through a tunnel that hadn't yet been built? That's one problem. Archeological remains also raise a second question.

Hezekiah's tunnel is still there. And it's a crazy piece of engineering. It lurches about, piercing hard rock and missing softer stuff -- adding needless excavation. Archeologists have made every excuse for bad design. Hezekiah, after all, worked under the stress of a siege.

An inscription adds to the problem. It tells how workers tunneled from opposite directions:

On the day of the piercing through, the stone-cutters struck through each to meet his fellow, axe against axe. Then ran the water from the spring to the pool for 1200 cubits, and a hundred cubits was the height of the rock above the head of the stone-cutters.

Now why would anyone in his right mind cut a channel that high!

Israeli geologist Dan Gill looks at the tunnel in its geological context. He sees what others missed. This is terrain where you find Karst formations. It's a limestone deposit, shot through with water-carved caves.

Suddenly it all comes clear. David got into the city through a series of limestone caves. Long afterward, Hezekiah straightened out those caves. He did some tunneling to connect with the Spring, But he also used what was already there.

So we learn again not to underestimate our forbears. Hezekiah built this old waterworks under battle conditions. He followed the flow of the land. He left a marvel of adaptive civil engineering. And it's still there to see, 2700 years later.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Gill, D., Subterranean Waterworks of Biblical Jerusalem: Adaptation of a Karst System. Science, Vol. 254, 6 Dec. 1991, pp. 1467-1471.

The Old Testament describes David's entry into Jerusalem in 2 Samuel 5:8. Hezekiah's tunnel turns up in 2 Kings 20:20; Isa. 22:9,11; 2 Chron. 32:2-4; 2 Chron. 32:30; Ben Sira (Ecclesiasticus) 48:17.

I am grateful to listener George Hollenback who notes that out the hundred-cubit height of the tunnel is a misreading of the Hebrew. Actually, it refers to the depth of the tunnel -- a hundred cubits was the distance from the tunnel ceiling to the highest point above the tunnel

He quotes a later work by Dan Gill: How They Met: Geology Solves the Mystery of Hezekiah's Tunnelers. Archaeology Review, Vol. 20 No. 4 July/August 1994. This article shows a compressed cross section through the straightened length of the tunnel and, according to the scale shown, the average height of the tunnel is about two meters, with a maximum of about five meters near the Siloam pool end.

The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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