sorry, I read it as loose grain used as base for amphorae, not as grain in jars.
Yeah, the waterproofed plugs retained integrity even after being submerged for so long.
I’m sorry too, you inferred right, imho the grain went right into the “hollow ship” and was used to nest the amphorae, lower the center of gravity, stabilize the ship, and increase the proceeds on the voyage. The neck holes were indeed “corked” and sealed, and the captain and crew would deal off the amphorae to whomever came by and was interested. The buyer lugged the product after sale. Probably very few whole-cargo sales, unless loaded with a homogeneous cargo that was in demand right then.
Rome banned the daytime use of carts because the city (unlike its colonies) was an unplanned warren of narrow alleys and streets, so cargo in Rome itself would move at night.
The racks idea looks great until the liquid shifting inside each jug worsens the rolling of the ship, not to mention that the weight of the contents of the jugs (as well as the rather heavy jugs themselves) would break or break out of the proposed flimsy (and as far as I know, unattested) frames. As TigersEye noted above, some amphorae held 80 gallons or more, hence over 600 pounds of liquid.
Thanks to all, *great* discussion so far, nice pics, and ‘Civ kisses to GraceG and Red Badger. ;’)