The Berlin Defence, also called the Berlin Wall, is a chess opening that begins with the moves:
The opening is a variation of the Ruy Lopez and is assigned codes C65-C67 in the Encyclopaedia of Chess Openings. The code C65 covers White moves other than 4.0-0, such as 4.d3 (4.Nc3 is considered a variation of the Four Knights Game). The code C66 covers the variation 4.0-0 d6, and the code C67 covers the variation 4.0-0 Nxe4 (usually regarded as the main line of the Berlin Defence)
The most common fourth move for White, which leads into the main lines of the Berlin, is 4. 0-0. The typical continuation is ...Nxe4 5. d4 Nd6 6. Bxc6 dxc6 7. dxe5 Nf5 8. Qxd8+ Kxd8 (sometimes called the l'Hermet variation), which was played in all four Berlin games of the Classical World Chess Championship 2000. The queens are exchanged off the board early, leading to a position that is difficult for White to win. Vladimir Kramnik assesses the endgame as better for white, but believes that this advantage is usually insufficient to win and that Black should be able to draw. Black's alternatives are generally regarded as inferior, such as 4...d6 which is considered too passive, and 4...Bc5 which allows white to play 5.Nxe5 (preparing to respond to 5...Nxe5 with 6.d4) or 5.c3.
An increasingly popular option for players who wish to avoid this line is 4.d3, known as the Anti-Berlin. This line avoids exchanging off the queens early in the game and so sidesteps the traditional Berlin endgame. Black typically responds 4...Bc5 or less commonly 4...d6. 4...Ne7 is the Mortimer Trap, which wins a piece if white plays 5.Nxe5, but is regarded as an inferior move because it loses time by moving the same piece twice.
White can also play 4.Nc3, which transposes to the Four Knights Game. Black can then play 4...Bb4 (the Symmetrical Variation), 4...Nd4 or less commonly 4...Bd6. The resulting position is generally judged as relatively quiet and positional, with roughly equal chances for both sides.
Other than 4.0-0, 4.d3 and 4.Nc3, other fourth moves for White are rarely seen.
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