A Sluice Gate in Hezekiah’s (Iron Age II) Aqueduct in Jerusalem: Archaeology, Architecture and the Petrochemical Setting of Its Micro and Macro Structures

As part of an important and unique engineering project to protect access to the only perennial source of water in Iron Age II Jerusalem, the engineers of the Israelite king Hezekiah (~715 - 686 BCE) excavated a 533-m-long-subterranean water conduit. His reign took place during a time when the Assyrian empire was consolidating its control of Palestine and Syria, and the threat to the city’s only major water supply was acute and immediate. The aqueduct was constructed to transfer water from the Gihon spring, on the western flank of the Kidron Valley in NE Jerusalem, into the Siloam pool—a water reservoir built during the Middle Bronze II (MB II) Period and located inside the southeastern edge of the city. Hezekiah’s engineers were well aware that such a diversion of water from the northern spring source south into the Siloam pool would lower the water level not only in the immediate environs of the Gihon spring cave but also from the main reservoirs and water conduits. It would thereby threaten the water sources supplying the city’s religious and political heart. To deal with the problem a “device” to control water level in the new aqueduct and thereby also the spring environ was designed and eventually constructed about 71 m from the tunnel’s southern exit. This was where the tunnel ceiling rises rapidly from a height of ~2 m and reaches almost 6 m at the tunnel exit. Two parameters were decisive in the design and choice of this location 1) a threat to the city’s security and 2) the necessity to exercise control of the sluice system from without. Prior to tunnel inauguration four iron bolts > 8 cm in length and up to 1.2 cm wide, were hammered at about waist height through wood panels into which a wooden gate (the sluice) was fitted. A cable, probably woven of wool fiber, raised and lowered the gate. We retrieved and studied two of the four iron bolts and discovered that they are partially enveloped with accreted slivers of (apparently) cedar wood, now petrified to iron hydroxide. We have studied the bolts by SEM-EDS and XRD and were able to unravel a long history of oxidation of metallic iron during which the phases goethite, lepidocrocite, magnetite and lastly akaganeite crystallized—in that order. Collectively these species testify to corrosion of nails during a long history of a fluctuating, occasionally unique, chemical environment within the microcosm of the bolts and probably along the full length of the aqueduct. The external morphology of the bolts and the chemical composition of the metallic iron imply smelted low carbon wrought iron,