This is the Ruy Lopez or Spanish Game. White's idea is simple: he attacks the piece
which defends the e-pawn. There is no immediate threat, as ...Qd4 or ...Qg5 would
answer 4.Bxc6 dxc6, but once White protects e4 this attack against e5 must be dealt
with.
The lines of attack and defense which spring from this position have fascinated
chessplayers for centuries.
