"The nigiri and tuna rolls we eat today are a far cry from the pungent, rice-less, barrel-fermented stuff that originated during the 3rd century B.C."
At First We Feast, an illustrated history of sushi with illustrations by Albert Hsu. Above, Nare-Sushi:
Basically: Barrel-fermented fish with rice. Rice is scraped off. Only the fish is eaten.
Originated: 3rd century B.C. in Southern China
Preparation time: 1 year
Where to get it today: Regions near Lake Biwa