[The_Victor]

There obviously must be a reason that escapes me, but I’ve always been puzzled by the purpose in the design of a liquid storage container that cannot stand upright on it own.

[SunkenCiv]

I think it had to do with the method by which it was made. Also, aboard ship, the jars would be stuck down into something, like straw, or more likely grain. When such ships got into duress, bailing probably wouldn't help, but the ships were much easier to abandon; I'd imagine a lot of crews survived such founderings, grabbing whatever was handy as a floatation device. There must be a good number of intact wrecks, as Ballard's team found in the Black Sea, down below the anoxia level.

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[buffaloguy]

“There obviously must be a reason that escapes me, but I’ve always been puzzled by the purpose in the design of a liquid storage container that cannot stand upright on it own.”

The bottom of the jars fit into racks which had holes in them. Much more secure than a flat bottomed jar on a pitching ship.