Played on 3 stacked 6x8 boards. The two armies are not the same. The Persians line up the FIDE pieces: 18 Pawns, 4 Knights, 4 Bishops, 2 Rooks, 1 Queen and 1 King. The Spartans field 18 Hoplits, 4 Captains, 4 Lieutenants, 1 Cardinal, 1 Crowned rook and 2 Kings. Thirty men each.
Pawns move like orthodox pawns on their current plane, but can go to another plane for captures only (see figure).
Knights move following L shape paths in the 3 dimensions. They land on the opposite color from the starting cell.
Bishops move following 3D diagonals always remaining on the same color.
The Queen moves like Rook + Bishop + Unicorn.
The King moves like orthodox King on its current plane, but can go to another plane for captures only (see figure).
The Hoplit is the mirror image of the Pawn: it moves where the Pawn captures, and captures where the Pawn moves. It steps 1 square diagonally forward on its plane, and captures 1 square straight ahead on its plane, or 1 square diagonally forward on the plane above or below. From its initial square it may also jump 2 squares diagonally forward to an empty square.
Moves and captures 1 or 2 steps (jumping) orthogonally or on the column.
Moves 1 step sideways on its plane without capturing. Moves and captures 1 or 2 steps (jumping) diagonally on its plane, or by the upper or lower corners, changing level and square color at the same time.
Combines the move of the bishop and the knight.
Combines the move and capture of the rook and the king.
Sparta is a diarchy, and its two Kings are both royal. Each moves like the FIDE King: orthodox King on its own plane, another plane for captures only.
A check on a single King is not binding. The Spartans may ignore it, and may leave that King to be captured: the game goes on. Only a duple check, both Kings attacked at the same time, has to be answered, and the Spartans may never move into one. Once a single King is left, check and checkmate are ordinary again, and the Spartans lose when that last King is checkmated.
A Pawn reaching the far rank promotes to Knight, Bishop, Rook or Queen. A Hoplit reaching the far rank promotes to Captain, Lieutenant, Cardinal or Crowned rook - and, if one of the two Spartan Kings has been captured, it may be promoted to King instead. The Spartans never have three Kings.
Double move for Pawns and Hoplits (start): yes.
Castling: Persians only, no Spartan piece castles.
"En passant" capture: yes.