This game was invented by an inhabitant of Marseilles, but it is not for certain whether this was Albert Fortis, together with the Norwegian J. Rossolow (who was then in the city), or by Jehan de Queylar. The origin of the game dates somewhere between World War I, and 1925.
Famous chess players who are said to have played this variant are: Alekhine, Reti, Znosko-Borovsky, and Cheron. It also still is popular in organisations as AISE and NOST.
All rules of normal chess apply, but with the following modification. Each turn, a player makes two moves. He may move either twice with the same piece, or make moves with two different pieces. Castling counts as one move.
If a player gives check on its first move in a turn, he moves only once that turn. A player in check must remove the check in the first half of his turn. A player may not move his king into check, also not on the first half of his turn.
A pawn that is moved two squares in one move (half a turn) can be taken en-passant, even if the pawn moved in the first half of the turn. The en-passant taking should be done on the first move of the turn. However, when two pawns can be taken en-passant, this is allowed.
To reduce whites opening advantage, Robert Bruce suggested in 1963 the following simple rule change: on his first turn, white only makes a single move. This rule change found wide acceptance, and usually is preferred above the unbalanced variant. The balanced variant is called Balanced Marseillais Chess, but often the `balanced' is just omitted from the title of the game.