C55 Italian Game: Two Knights

ECO code C55 covers the Two Knights Defence after 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6, in the branches where White avoids the sharp knight jump to g5 against f7. The quiet 4.d3 protects e4 and prepares a slow build-up with c3, Re1 and a later d4. Black can answer with 4...Be7, as in the line with 5.O-O, or with 4...h6, which rules out Ng5 and Bg5. The more direct 4.d4 opens the centre at once. After 4...exd4 5.e5 d5, Black does not retreat the attacked knight. Instead Black strikes at the bishop on c4, frees the c8-bishop and prepares to plant the knight on e4.