A lead sounding weight
Herodotus says that when you are still a day's sail from Egypt, you can drop a sounding line and bring up mud from eleven fathoms. The lead told a pilot how deep the water was, and what came up with it told him where he was.
What it was
A heavy lead weight shaped like a bell or a cone, on a long rope knotted or marked at intervals. You threw it over the bow, let it run to the bottom and counted the rope. Lead sounding weights turn up in quantity on Greek and Roman wrecks, because lead does not rot and nobody bothers to salvage a lump of it from the seabed.
Reading the bottom
Many of these weights have a hollow in the base. The usual explanation, taken from much later sailors, is that the hollow was packed with tallow so that sand, shell or mud stuck to it and came up with the lead. For the ancient weights that is a sensible inference rather than something an ancient writer says. What Herodotus does say is that the Nile's mud reaches far out to sea, and that you can tell you are nearly there by what the line brings up.
And Odysseus
Odysseus had twelve ships when his wanderings began. In the Odyssey he crosses open sea by the stars, keeping the Great Bear on his left hand, as Calypso told him to. A sounding lead is for the other end of a voyage: the last day, when you are looking for land you cannot see yet.
- Herodotus 2.5.2: a day's sail from Egypt, a sounding line brings up mud at eleven fathoms
- Acts 27:28: sounding twenty fathoms, then fifteen, before the shipwreck on Malta
- Homer, Odyssey 9.159–160: the twelve ships; 5.270–277: steering by the stars
- Oleson, 'Ancient Sounding-Weights: A Contribution to the History of Mediterranean Navigation', Journal of Roman Archaeology 13 (2000)
- Picture: made with AI for The Ember Atlas, an imagining, not a record of how it looked.