Spartan Chess is a chess variant where two different entirely armies combat each other.

The Persian army (white) is the normal FIDE army (which, as we know, was brought to us via Persia). The Spartans (black) are ruled by two Kings, of which at least one must be ounattacked after your turn. But the other can be sacrificed (and then re-obtained by promotion). All other Spartan pieces, including the Hoplit 'Pawns', are unorthodox pieces.