http://en.m.wikipedia.org/wiki/Kyrenia_ship
Ten different types of amphorae were discovered in the wreck called the Kyrenia ship. A good deal more about the ship and its intact cargo is available there.
They were able to salvage a large portion of the ship, sufficient in fact to build several replicas.
So it seems as the methods of securing the amphorae varied.
Now as to those found in Brazil...drunken space cadets on leave might not be so outlandish after all.
;>)