C67 Ruy Lopez: Berlin Defence

ECO code C67 covers the Berlin Defence of the Ruy Lopez after 1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.O-O Nxe4, where Black takes the e4-pawn and expects White to win it back. The main branch is 5.d4 Nd6 6.Bxc6 dxc6 7.dxe5 Nf5 8.Qxd8+ Kxd8, the Berlin Wall Endgame. Black loses the right to castle and has doubled c-pawns but owns the bishop pair and a solid structure, while White aims to use the kingside pawn majority. Other branches include 6.dxe5 Nxb5 7.a4, the l'Hermet Variation, and 5.Re1 Nd6 6.Nxe5 Be7, where White regains the pawn with pieces still on the board.