The Berlin variation of the Spanish is one of the most popular chess openings among world-class players. After 1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 Black can play a completely sound opening based mainly on understanding rather than memorizing theory. Many opening books make this claim, but the scarcity of forcing lines in the Berlin mean that in this case it is true. The trick is to gain the requisite understanding, and this is where John Cox's eloquent prose comes into its own. After reading his explanations it will be clear why this robust opening has been nicknamed The Berlin Wall.