Jerusalem’s Ancient Aqueducts

The big trench outside Jerusalem’s Jaffa Gate has aroused local curiosity for many months. The designers of the grand Mamilla Project, engaged in reshaping the Old City’s western approaches, have discovered to their consternation that ancient urban planners had pre-empted them. Unexpected ruins—some apparently over 2,000 years old—have come to light. Giant mechanical earth-movers and the archaeologist’s bucket and trowel have incongruously and uncomfortably worked alongside each other as the future and the past vie for control of the project’s final image. ‘Responsible authorities’ have decided what is worthy of preservation in a small park, and what is to be sacrificed to progress.

The archaeologists have exposed an ancient aqueduct. Its unobtrusive simplicity belies a complex and intriguing historical conundrum. The water needs of ancient Jerusalem rapidly outgrew its original source, the Gihon Spring. By the first century B.C. even the private cisterns and public reservoirs that trapped the winter rains were not enough. The solution was to exploit a number of fairly small springs in the Judean hills south of Jerusalem. The key to the system was a series of three huge reservoirs, on the high road south of Bethlehem, known today as Solomon’s Pools.

The exact dating of each of the pools is difficult, but it is generally accepted that the middle pool, with its capacity of 90,000 cubic metres, is the oldest, probably built by King Herod 2,000 years ago. It collected the water of two local springs. The Low-Level Aqueduct, as the channel became known, snaked around the hills, following the natural contour lines.

Only in two places did it shorten its route by boring through hills: in Bethlehem and below the Hill of Evil Counsel. It descended some­where in the area of Yemin Moshe, crossed the Hinnom Valley at Sultan’s Pool and swung south and east around Mount Zion before entering the city. Its rock-hewn trench (with later Ottoman clay pipes) can still be seen above the steps which descend from the Jewish Quarter to the Western Wall. Passing over Wilson’s Arch (within the men’s side of the Western Wall) it ended its twenty-one-kilometre route in the cisterns of the Temple Mount.

The ancient Jewish historian Josephus Flavius tells of the undertaking of the notorious first-century Roman procurator Pontius Pilate to bring a current of water to Jerusalem”. Scholars believe that Pilate’s undertaking was a new conduit, which fed the reservoir at Solomon’s Pools from a cluster of springs at Arrub to the south, thus doubling the capacity of the Low-Level Aqueduct. The Arrub Aque­duct is the gem of the system. It followed the contour lines in unusually well-made rock-hewn and built-up channels, three tunnels through solid rock, and dropped a mere forty-five metres over its forty-kilometre length, an almost unheard of gradient of one-per­thousand.

By the second century A.D. Jerusalem was a very different city. The temple was gone, the Jewish population banished, and the city rebuilt as the pagan Aelia Capitolina. The Low-Level Aqueduct was, if not redundant, at least inadequate for a town centred on the high ground inside today’s Jaffa Gate. The Roman solution to the problem was a high-level aqueduct no less ingenious than its low-level predecessor. The source was a modest spring at the head of Wadi el-Biyar.

The Romans built a dam at the valley’s lower end to back up the winter run-off. A three-kilometre tunnel from the spring to the dam drew in water from its sodden surroundings. By the time it emerged as a surface aqueduct, its flow was considerably enhanced. The Biyar Aqueduct fed into the highest of Solomon’s Pools. From that reservoir the Roman Tenth Legion built the new high-level aqueduct to Jerusalem in a virtually straight line. A siphon system of tightly interlocked stone rings—many still seen today—stretched for three kilometres through the depression and up the other side. Beyond this point researchers have found no trace of the aqueduct. Its direction and superior elevation, however, leave little doubt that its destination was the area of the Jaffa Gate, perhaps the Hezekiah’s Pool visible from the top of the Tower of David.

Here lies a conundrum. Captain Charles Wilson of the Royal Engineers, who conducted an ordnance survey in Jerusalem in 1865, wrote of “a conduit” from the Mamilla Pool “which passes under the city wall a little to the north of the Jaffa Gate”. That conduit was still identifi­able as recently as 1926 when Canon Hanauer wrote his Walks Around Jerusalem.

Whether the newly discovered water-channel is part of the long sought high-level aqueduct, or some less dramatic local system, is still a moot question which further digging might answer. One can only agree, however, with the judgement of the great Victorian scholar George Adam Smith on Jerusalem’s ancient water systems : “Among all the remains none are so impressive as these vast and intricate monuments from every stage of the history”.