Rook (chess)

The rook (; ♖, ♜) is a piece in the game of chess resembling a castle. Formerly the piece (from Persian رخ "rokh"/"rukh", meaning chariot) was alternatively called the "tower", "marquess", "rector", and "comes" ("count" or "earl") . The term "castle" is considered to be informal, incorrect, or old-fashioned.
Each player starts the game with two rooks, one on each of the corner squares on their own side of the board.
Placement and movement.
The white rooks start on squares a1 and h1, while the black rooks start on a8 and h8. The rook moves horizontally or vertically, through any number of unoccupied squares (see diagram). The rook cannot jump over pieces. As with captures by other pieces, the rook captures by occupying the square on which the enemy piece sits. The rook also participates, with the king, in a special move called castling.
Strategy.
Relative value.
The rook is worth about 5 pawns. In general, rooks are stronger than bishops or knights (which are called "minor pieces") and are considered greater in value than either of those pieces by nearly two pawns but less valuable than two minor pieces by approximately a pawn. Two rooks are generally considered to be worth slightly more than a queen (see chess piece relative value). Winning a rook for a bishop or knight is referred to as winning "the exchange". Rooks and queens are called "heavy pieces" or "", as opposed to bishops and knights, the minor pieces. 
Development.
In the opening, the rooks are blocked in by other pieces and cannot immediately participate in the game, so it is usually desirable to "connect" one's rooks on the first by castling and then clearing all pieces except the king and rooks from the first rank. In that position, the rooks support each other and can more easily move to occupy and control the most favorable .
A common strategic goal is to a rook on the first rank of an open file (i.e., one unobstructed by pawns of either player) or a half-open file (i.e., one unobstructed by friendly pawns). From this position, the rook is relatively unexposed to risk but can exert control on every square on the file. If one file is particularly important, a player might advance one rook on it, then position the other rook behind—"doubling" the rooks.
A rook on the seventh rank (the opponent's second rank) is typically very powerful, as it threatens the opponent's unadvanced pawns and hems in the enemy king. A rook on the seventh rank is often considered sufficient compensation for a pawn . In the diagrammed position from a game between Lev Polugaevsky and Larry Evans, the rook on the seventh rank enables White to draw, despite being a pawn down .
"Two" rooks on the seventh rank are often enough to force victory by the blind swine mate, or at least a draw by perpetual check.
Endgame.
Rooks are most powerful towards the end of a game (i.e., the endgame), when they can move unobstructed by pawns and control large numbers of squares. They are somewhat clumsy at restraining enemy pawns from advancing towards promotion, unless they can occupy the file behind the advancing pawn. As well, a rook best supports a friendly pawn towards promotion from behind it on the same file (see Tarrasch rule).
In a position with a rook and one or two minor pieces versus two rooks, generally in addition to pawns, and possibly other pieces – Lev Alburt advises that the player with the single rook should avoid exchanging the rook for one of his opponent's rooks .
The rook is a very powerful piece to deliver checkmate. Below are a few examples of rook checkmates that are easy to force.
History.
In the medieval shatranj, the rook symbolized a chariot. The Persian word "rukh" means "chariot", and the corresponding piece in the original Indian version, chaturanga, has the name "ratha" (meaning "chariot"). In modern times it is mostly known as हाथी (elephant) to Hindi-speaking players, while east-Asian chess games such as xiangqi and shogi have names also meaning chariot (車) for the same piece.
Persian war-chariots were heavily armored, carrying a driver and at least one ranged-weapon bearer, such as an archer. The sides of the chariot were built to resemble fortified stone work, giving the impression of small, mobile buildings, causing terror on the battlefield.
In Europe the castle or tower appears for the first time in the 16th century in Vida's 1550 "Ludus Scacchia", and then as a tower on the back of an elephant. In time, the elephant disappeared and only the tower was used as the piece.
In the West, the rook is almost universally represented as a crenellated turret. The piece is called "torre" ("tower") in Italian, Portuguese, Catalan and Spanish; "tour" in French; "toren" in Dutch; "Turm" in German; "torn" in Swedish; and "torni" in Finnish. In Hungarian it is "bástya" ("bastion") and in Hebrew language it is called "צריח" (pronounced "Tzariach", meaning "fortified tower"). In the British Museum's collection of the medieval Lewis chess pieces the rooks appear as stern warders, or wild-eyed Berserker warriors.
Rooks usually are similar in appearance to small castles, and as a result a rook is sometimes called a "castle" .
Modern chess literature rarely, if ever, uses this term.
In some languages the rook is called a ship: Thai เรือ ("reūa"), Armenian Նավակ ("navak"), Russian ладья ("ladya"), Javanese ꦥꦿꦲꦸ ("prahu"). This may be because of the use of an Arabic style V-shaped rook piece, which some may have mistaken for a ship. It is possible that the rendition comes from Sanskrit "roka" (ship); however, no "chaturanga" pieces were ever called a "roka". Murray argued that the Javanese could not visualize a chariot moving through the jungles in sweeping fashion as the rook. The only vehicle that moved in straight fashion was ship, thus they replaced it with prahu. Murray, however, did not give an explanation of why the Russians call the piece a "ship".
Peter Tyson suggests that there's a correlation between the name of the piece and the word "rukh", a mythical giant bird of prey from Persian mythology. 
In Bulgarian, it is called the cannon (Топ, Romanised "top").
In Kannada, it is known as ಆನೆ ("āāne"), meaning "elephant". This is unusual, as the term for "elephant" is in many other languages applied to the bishop.
Heraldry.
 Chess rooks frequently occur as heraldic charges. Heraldic rooks are usually shown as they looked in medieval chess-sets, with the usual battlements replaced by two outward-curving horns. They occur in arms from around the 13th century onwards.
In Canadian heraldry, the chess rook is the cadency mark of a fifth daughter.
Unicode.
Unicode defines two codepoints for rook:
♖ U+2656 White Chess Rook (HTML &#9814;)
♜ U+265C Black Chess Rook (HTML &#9820;)