Today, a relatively inexpensive G.P.S. receiver can indicate the position of a ship within a few meters, and moving charts on a video screen facilitate navigation. Until relatively recently, however, the compass was not particularly accurate, and navigators were dependant on charts of widely varying accuracy. Since the depth of water beneath a hull is always a primary concern, the sounding-weight—known in the Mediterranean by at least the sixth century B.C.—remained a critical navigational aid on seas and rivers well into the twentieth century. A sounding-weight is a roughly bell-shaped mass—usually made of lead—averaging about five kilogrammes in weight, with a sturdy attachment lug at its apex and a tallow cup in its spreading base. Ancient mariners used sounding-weights, the oldest known marine navigational instrument, not only to determine the depth of water, but also to bring up samples of the bottom, comparing the result with their knowledge of coastal geography and river behavior. Although charts were rudimentary by modern standards, Greek and Roman navigators had a surprisingly effective knowledge of the seas. Over the past ten years I have explored the history of the sounding-weight in the Classical world and the evidence (drawn from my new corpus of sounding-weights) this artifact supplies concerning the navigational techniques and charts that facilitated Greek and Roman navigation within the Mediterranean Sea and far beyond it. I am trying to  reconstruct the origins and development of the humble sounding-lead in the Classical world, its typology, the history of its use in Mediterranean waters, and the reasons for its continued employment only a few years ago. My corpus of Greek and Roman sounding-leads now includes over 180 examples. I started out believing that the majority of these weights would be isolated finds without any archaeological context, but in fact approximately 50 percent of the weights in my corpus can be dated from an associated shipwreck or other context. I have constructed a typology of shapes (plate 1, plate 2, plate 3), and as the corpus grows, it should be possible to date even isolated specimens approximately. As my corpus becomes larger, I am shifting my attention to the place of sounding-weights in navigational technique.

For further information about my project, see the following publications:

E. Galili, J.P. Oleson, B. Rosen, "A Group of Exceptionally Heavy Ancient Sounding Leads: New Data Cponcerning Deep-Water Navigation in the Roman Mediterranean," Mariner's Mirror 96 (2010) 136-48.

J.P. Oleson, "Ancient Lead Circles and Sounding-Leads from Israeli Coastal Waters," Sefunim: Bulletin of the National Maritime Museum of Israel 7 (1988) 27-40.

J.P. Oleson, "An Ancient Lead Sounding-Weight in the National Maritime Museum," Sefunim: Bulletin of the National Maritime Museum of Israel 8 (1994) 29-34.

J.P. Oleson, "Herodotus, Mark Twain and Early Navigation," Resolution, Journal of the Maritime Museum of British Columbia 38 (Summer 1996) 19-20.
J.P. Oleson, "Ancient Sounding-weights: a contribution to the history of Mediterranean navigation," Journal of Roman Archaeology 13 (2000) 293-310.

J.P. Oleson “Herodotus, Aristotle, and Sounding Weights: The Deep Sea as a Frontier in the Classical World,” pp. 32-48 in T. P. Tassios, C. Palyvou (edd.), Ancient Greek Technology: Proceedings of the 2nd International Congress. Athens: Technical Chamber of Greece, 2006.

J.P. Oleson, “Testing the Waters: The Role of Sounding-Weights in Ancient Mediterranean Navigation.” Pp. 119-76 in R.L. Hohlfelder, ed., The Maritime World of Ancient Rome. Memoirs of the American Academy in Rome, Suppl. 6. Ann Arbor: University of Michigan Press, 2008.

The 2008 publication, which can be downloaded as a pdf file here, includes a full discussion of the history and significance of this artifact, it relationship to both navigation and the history of the exploration of the deep sea in antiquity, and a corpus of ancient sounding weights current to May 2007. Since that time I have found information on approximately 10 further weights. Several articles are in preparation at this time.