a tactic in itself because the piece that moved could attack or otherwise threaten another piece. The opponent has to get out of the discovered check on the following move and may not be able to also thwart the attack by the other piece that moved. Double check. A double check is a check from two pieces to the opponent's king in a single move. This happens when a moved piece attacks the king, resulting in a second piece giving check by discovered check. It can also happen, though very rarely, when an en passant capture opens two lines of attack simultaneously. A double check cannot be blocked, nor can it be met by capturing one of the checking pieces (unless the king itself makes the capture), because both checking pieces cannot be captured or blocked in one move. Therefore, a double check forces the king to make a move. In algebraic chess notation, a double check move is sometimes noted with a "++" after the written move in place of the usual "+", although "++" has been used to indicate checkmate (along with "#"). Cross-check. When a check is answered by a check, particularly when this second check is delivered by a piece blocking the first, it is called a cross-check. In fact, a "cross-checkmate" is also possible in that way (that is, to answer a check with a checkmate); but since no such term is in common use, it would be called cross-check as well. Announcing check and notation History The idea of warning that the king was under attack (announcing "check" in modern terminology) is present in the earliest descriptions of chess rules, in Persian/Arabian manuscripts. 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 . In this usage, the words "check" and "chess" come via Arabic from Persian shāh, meaning "king" or "monarch" . Less commonly (and obsolete), the warning garde can be said when a player directly attacks the opponent's queen in a similar way. This was mostly abandoned in the 19th century . A move can be both check and garde simultaneously. Before the queen acquired its current move (about 1495) the rook was the most powerful piece. At that time