The oldest known tunnel at which two teams advanced simultaneously is the Siloam tunnel in Jerusalem, completed around 700 BC. It has been posited that it was dug by maintaining depths close enough to the surface of the solid karst that the diggers could hear loud banging from the surface guiding the two teams towards one another. Frumkin, Amos; Shimron, Aryeh (2006). "Tunnel engineering in the Iron Age: Geoarchaeology of the Siloam Tunnel, Jerusalem". Journal of Archaeological Science. 33 (2): 227–237. doi:10.1016/j.jas.2005.07.018.
