Gabriel Maura, from Puerto Rico, invented this game in 1968. According to Pritchard, who describes this game, the game attracted several followers, until 1983, after a serious illness of the inventor. The game has been popular among players in Puerto Rico, Spain, Central America, and South America. Tournaments, including world championships were organised by FEMDAM, an international organisation. FEMDAM stands for: FEderación Mundial De Ajedrez Moderno (which is Spanish for 'World Federation of Modern Chess').
The game is played on a 9 by 9 board, which is checkered with a black square in the left corners. Opening setup is as follows:
King e1; Queen f1; Minister d1; Rook a1, i1; Knight b1, h1; Bishop c1, g1; Pawn a2, b2, c2, d2, e2, f2, g2, h2, i2.
King e9; Queen d9; Minister f9; Rook a9, i9; Knight b9, h9; Bishop c9, g9; Pawn a8, b8, c8, d8, e8, f8, g8, h8, i8.
Rook, knight, bishop, king, and queen move as in usual chess. When castling, the king always moves two squares in the direction of the rook. Pawns move as in orthodox chess, and can promote to queen, bishop, knight, rook or minister.
The minister has the combined moves of bishop and knight.
Since both Bishops start on dark squares, Gabriel Maura added a Bishop Adjustment Rule, which appears on page 32 of his 1973 'Tesis Matemática del Ajedrez Moderno' (Mathematical Thesis for Modern Chess):
It consists in exchanging the square of one of the Bishops with either of the adjacent major pieces - the Queen or the Queen's Knight on the right, or the Minister or Minister's Knight to the left - as long as neither of the pieces being exchanged has been moved from its original square.(Retrieved and translated by Jose Carrillo.)
The player would have four ways to do the adjustment, but he is only allowed to do it one time throughout the game, if he wishes to. This adjustment counts as a move, just like castling. The notation for it is: B=MN (example for the adjustment with the Minister's Knight).
Other rules are as in orthodox chess.