C48 Four Knights Game

After 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Bb5, ECO code C48 covers the Spanish Variation of the Four Knights Game. White develops the bishop as in the Ruy Lopez, pinning the knight on c6 that guards e5, and keeps castling and a later d4 in reserve. Black's most direct answer is 4...Nd4, the Rubinstein Counter-Gambit. The knight jumps into the centre, challenges the bishop and offers the e5-pawn. If White takes it with the knight, Black aims for quick, active piece play with ...Qe7 or ...Bc5. Quieter replies such as ...Bb4 lead to a symmetrical, slow-moving centre.