THE PROOF IS IN THE PLASTER. The flow of water causes sediment to accumulate over time on the surface of Hezekiah’s Tunnel. Vertical core samples taken from the floor of the tunnel show that, although fine layers of sediment cover the plaster on the surface of the tunnel (which in some places was plastered over several times in antiquity), there was no such sedimentary buildup beneath the earliest level of plaster (see section drawing and photo), demonstrating that water had not flowed over the surface in a natural karst stream before the plaster was laid after the excavation of the tunnel. Carbon-14 tests on twigs preserved in this early layer of plaster confirm that the tunnel was excavated in the eighth century B.C.E.