The board, marked with a grid of 19 lines by 19 lines, may be thought of as a piece of land to be shared between the two players. One player has a supply of black pieces, called stones, the other a supply of white. The game starts with an empty board and the players take turns, placing one stone at each turn on a vacant point. Black plays first, and the stones are placed on the intersections of the lines rather than in the squares. Once played, stones are not moved. However they may be surrounded and so captured, in which case they are removed from the board as prisoners.