Millet. Farmed in Greece from the Bronze Age, and in other hot climates, it's often a main ingredient in bird seed in Western Countries, but is currently having something of a revival for its low price and health benefits, some even say Greek Millet Is The New Quinoa.
The word 'millet' in Greece refers to how the Ottomans classed various 'nations' under their rule, each with its own rules (and taxes). Eastern Orthodox Christians belonged to the Rūm millet (as in 'Rome').
Image by Claus Rebler