Berlin Defence (chess)

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)
History.
The opening was first analysed in depth in the 19th century, and received its name from the Berliners that examined its variations. Due to the defensive and drawish nature of the opening, it is sometimes referred to as the Berlin Wall. The opening was rarely used in high level games and received little attention until the Classical World Chess Championship 2000, in which challenger Vladimir Kramnik used it as a drawing weapon against champion Garry Kasparov. Kramnik used the Berlin in games 1, 3, 9 and 13 in the match (each time as black), all four of which were drawn. After losing the match, Kasparov cited Kramnik's superior opening preparation as a reason for his loss. In an interview with John Henderson, Kramnik described his use of the Berlin:"The Berlin Defence suited my strategy for the match. I had a defensive strategy – Actually, I had in my pocket some other sharper stuff to fall back on – but first I wanted to try the defensive strategy with Black and it worked so well. This was all new to Kasparov – he probably expected me to fight for equality with Black."The 2000 match caused a resurgence of interest in the Berlin Defence at all levels of the game, such as its use by Magnus Carlsen and Viswanathan Anand in games 4, 6, 7 and 8 of the World Chess Championship 2013. It is now regarded as a solid opening for Black to use in order to achieve an equal endgame.
Basics.
Black's third move attacks the e4 pawn. However, it is not an actual threat, since if Black captures on e4 then White can win back the e5 pawn. Usually in the Berlin Defence, the players exchange queens early, causing the game to quickly enter an endgame. The resulting endgames are generally viewed as equal or very slightly favourable for White. Black has the disadvantage of doubled pawns and a king stuck in the centre, but has compensation in the form of the bishop pair. Strategically, the Berlin Defence is normally used as a drawing weapon by players who want to obtain a draw as Black, and by players who prefer to play defensively and reach endgames.
Statistics.
The chess database chessgames.com contains 9,264 games in which the Berlin Defence was played, making it the second-most popular variation of the Ruy Lopez and constituting about 17% of all Ruy Lopez games. Of the games in which it was played, 33.1% were wins for White, 22.4% wins for Black, and 44.5% drawn. The relatively high drawing rate of the opening compared to other lines has contributed to its reputation as a drawing weapon. For comparison, the overall rates for the Ruy Lopez are 36.7% wins for White, 24.7% wins for Black, and 38.6% drawn.
Main variations.
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.
Other than 4.0-0, 4.d3 and 4.Nc3, other fourth moves for White are rarely seen.