 One of the major differences between orthodox and circular chess in practice is in the opening.In orthodox chess, opening theory has developed over several centuries, and the use of computer analysis has resulted in top level games frequently not deviating from known theory until the 20th move or beyond; in circular chess, there is virtually no opening theory, and consequently players are "on their own" from the first move.In orthodox chess, advancing the king's or queen's pawn are generally considered the best opening moves, as doing so attacks two key central squares, opens a diagonal to enable the development of a bishop, and, in the case of the king's pawn, the queen also.