Like bishops, rooks are long range pieces that can have an influence even from the edge of the board. As with bishops, you should try to place your rooks on open lines where their firepower can be directed at the enemy. Rooks are more valuable than bishops and knights, so you should keep them in reserve in the early part of the game. Moving rooks out into the middle of the board too early can be a big mistake, as the enemy bishops and knights can attack your rooks and chase them about. A rook that goes on an adventure too early can easily become surrounded and trapped.
Rooks are strongest when they protect each other - this is known uniting or doubling rooks. You should try to unite your rooks along the back rank as early as possible. If you look at the starting position, you'll notice that the rooks are the only pieces on the board that are completely unprotected to begin with. Uniting rooks reduces the possibility of an unprotected rook being picked off by the enemy queen, and also helps to guard your back rank. Another reason to unite your rooks is so that they can compete with the enemy rooks for open files. Here is an example:
When your roooks have secured an open file, a common way to exploit it is to double your rooks on the file. This allows the front rook to move into the enemy camp while being protected by its comrade from behind. The firepower of the two rooks can also act as an effective battering ram agains the enemy position.
One of the most powerful attacking posts for a rook is on the seventh rank (the opponent's second rank). On the seventh rank, the rook attacks enemy pawns still on their starting squares, but it can also have a powerful restricting effect on the opponent's defences. If the enemy king is on his back rank (where he is usually to be found), the rook can restrict his movement in preparation for checkmate. The rook on the seventh can often cut the defence in two, as in the example below:
Doubled rooks on the seventh rank are even better, and are often decisive. While the enemy pawn shield can often fend off attacks from the front - for example, by advancing or defending from the side - it can be difficult to defend against an attack from the side.
The two rooks on the seventh rank are so strong, they can even save a draw when you're losing, by giving perpetual checks to the enemy king. Here is rather an exaggerated example to illustrate the point:
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