Hypogea 2015 - proceedings of international congress of speleology in artificial cavities - rome, marcH 11/17 2015 170 Introduction Ancient development of surveying techniques allowed water systems to be concealed underground, often using long tunnels (ForBeS, 1956). Bedrock tunnels connecting two points were often used as shortcuts across topographic barriers. Their construction involved relatively sophisticated surveying techniques, compared with subaerial aqueducts. Tunneling commonly involves three surveying stages: (1) subaerial survey between the two tunnel ends and designing the tunnel route; (2) transferring the planned directions to the underground; this may be performed through the tunnel entrances by measuring horizontal line of sight, and through narrow intermediate shafts; (3) surveying along the newly excavated tunnel segments. The surveying should be accurate enough to allow meeting of two excavating teams. Because of propagation of errors, which is inevitable in surveying, the two teams may miss the planned meeting point. Acoustic communication can be used to rectify this and finally meet the other team. The tunnels studied here were dug with the aid of intermediate shafts, each serving as a starting point for two excavation teams which met a team approaching from the opposite direction. The meeting point of the two teams and its close proximity provides us with an opportunity to directly measure the deviations associated with surveying errors. The horizontal deviations can be clearly deduced from modern maps of the ancient tunnels. The development of surveying techniques in the Hellenistic-roman period (e.g. vitruviuS, translated by MorGan, 1960) must have had an impact on tunnel surveying. Yet, actual usage of particular instruments is debatable, particularly in remote regions of the large empires. The observed deviations in tunnel construction may be used to determine the dispersal of new techniques. We study tunnels whose width is similar to that of humans, because wider tunnels may indicate later widening which can obliterate the signs of initial deviations. intermediate shafts are not a prerequisite for tunnel construction. Although using shafts in tunnel construction is an ancient technique, some tunnels without shafts predate the tunnels with shafts which are discussed below. some of the oldest water tunnels with intermediate shafts are known from the Assyrian empire (e.g. oLeSon, 2008). aSSurnaSipaL ii (884-859 Bce) built a canal which passed through a rock ridge at negoub via a tunnel seven km long, dug between pairs of vertical shafts. Assyrian tunnels were constructed SHAFTS ANd SUrVEY ErrOrS OF ANCIENT TUNNEL ENGINEErING IN JErUSALEM ANd CAESArEA wATEr SYSTEMS, ISrAEL Amos Frumkin Israel Cave Research Center (ICRC), Department of Geography, The Hebrew University of Jerusalem, 91905, Israel amos.frumkin@mail.huji.ac.il Abstract Ancient tunnels are some of the best sites to test ancient engineering techniques. several late Hellenistic (?) - roman period water tunnels in israel are studied in order to identify surveying problems associated with two types of shafts, inferred by deviations in the meeting points of the digging teams. in general, vertical shafts are better than inclined shafts in terms of tunnel survey and construction. However, there must be a reason why inclined shafts were preferred (over vertical ones) in some occasions. A possible reason for this could be the need for people to descend down the shafts for regular maintenance of the tunnel where this was needed. studied inclined shafts had steps which allowed easier access down the shafts into the tunnel. However, inclined shafts gave rise to surveying problems and associated deviations in the underlying tunnel. The meeting of the two digging teams could be assisted by acoustic communication, which was an ancient practice in israel, utilized already in iron Age (~700 Bce) tunneling. Keywords: water tunnel, survey errors, shaft, Jerusalem low-level aqueduct, caesarea water system. Riassunto Gli antichi tunnel sono fra i migliori siti per testare antiche tecniche di ingegneria. In Israele numerosi tunnel idraulici di età tardo ellenistica (?) - Romana sono stati studiati per individuare problemi associati a due tipi di pozzi, desunti dalle deviazioni nei punti di incontro delle squadre di scavo. In generale i pozzi verticali sono migliori di quelli inclinati ai fini della progettazione e della realizzazione. Tuttavia in alcune occasioni sono stati preferiti i pozzi inclinati rispetto ai pozzi verticali. Una possibile ragione potrebbe essere individuata nella necessità di raggiungere più facilmente il condotto sotterraneo per l’ordinaria manutenzione della struttura. I pozzi inclinati presi in esame presentavano gradini che permettevano un più facile accesso al tunnel ma potevano anche essere all’origine di problemi di rilievo e a relative deviazioni della galleria sottostante. L’incontro fra le due squadre di scavo potrebbe essere stato facilitato dal contatto acustico, che era un’antica pratica utilizzata in Israele per la realizzazione di gallerie già nell’ età del ferro (~ 700 a.C.). Parole chiave: tunnel idraulici, errori di indagine, pozzo, acquedotto di Gerusalemme bassa, sistema idrico Cesarea.