(c. 700–800) introduced the idea of warning that the king was under attack (announcing check in modern terminology). This was done to avoid the early and accidental end of a game. Later the Persians added the additional rule that a king could not be moved into check or left in check. As a result, the king could not be captured, and checkmate was the only decisive way of ending a game. With the spread of Islam, chess diffused into the Maghreb and then to Andalusian Spain. During the Islamic conquest of India (c. 12th century), some forms came back to India as well, as evidenced in the North Indian term māt (mate, derivative from Persian māt) or the Bengali borey (pawn, presumed derived from the Arabic baidaq). Over the following centuries, chess became popular in Europe, eventually giving rise to modern chess. Rules The initial setup in shatranj was essentially the same as in modern chess; however, the position of the white shah (king), on the right or left side was not fixed. Either the arrangement as in modern chess or as shown in the diagram were possible. In either case, the white and black shāh would be on the same file (but not always in modern India). The game was played with these pieces: Shāh ("king" in Persian) moves like the king in chess. Ferz ("counselor"; also spelled fers; Arabic firz, from Persian farzīn) moves exactly one square diagonally, which makes it a rather weak piece. It was renamed "queen" in Europe. Even today, the word for the queen piece is ферзь (ferz) in Russian, vezér in Hungarian, vezir in Turkish, vazīr in Persian and wazīr in Arabic. It has analogue to the guards in xiangqi. Rukh ("chariot"; from Persian rokh) moves like the rook in chess. Pīl, alfil, aufin, and similar ("elephant"; from Persian pīl; al- is the Arabic for "the") moves exactly two squares diagonally, jumping over the square between. Each pīl could reach only one-eighth of the squares on the board, and because their circuits were disjoint, they could never capture one another. This piece might have had a different move sometimes in chaturanga, where the piece is also called "elephant". The pīl was replaced by the bishop in modern chess. Even today, the word for the bishop piece is alfil in Spanish, alfiere in Italian, fil in Turkish, fīl in Persian and Arabic, and слон