The 4th Expansion is a new game board with Monasteries printed next to the play area.
It comes with 4 new boards numbered 13a to 13h (back to back 13a-13e, 13b-13f, 13c-13g, 13d-13h)
The following rules are then added to the basic game play of "The Castles of Burgundy":
As soon as a player creates a direct, straight connection between two monasteries with 5 connecting tiles on his game board, he earns 5 victory points.
The first player to complete all three connections between his monasteries wins an additional bonus of 5, 6, or 7 victory points (for a 2, 3, or 4 player game). The second player to complete all three connections wins 2-4 victory points.
This means that a player can win a maximum of 3x5 + 7 = 22 additional victory points over the course of one game.