Love the retort idea... many possibilities there.
....
Anyway, I've been reading 1491 (on my Kindle) ...and I'll have to get the quote, but....
Mulch!
That's the effect of the pottery!
Rain is what decimates the soils down there, leaching out the minerals as it drills down through un-canopied soil.
Pottery shards protect the soil from the relentless rain of ruin.
...as well as being a bit sponge-like & hosting beasties & providing buffering surfaces.
IMHO
