Ruy Lopez that after the common retreat 4.Ba4, Black will have the possibility of breaking a future pin on his by playing ...b5. White must take some care not to fall into the Ruy Lopez, Noah's Ark Trap, in which Black traps White's on the b3-square with a ...a6, ...b5, and ...c4 pawn advance on the . Ercole del Rio, in his 1750 treatise "Sopra il giuoco degli Scacchi, Osservazioni pratiche dell'anonimo Modenese" (On the game of Chess, practical Observations by an anonymous Modenese), was the first author to mention 3...a6. However, the move became popular after it was played by Paul
Four Knights Game attempt for White to exploit the advantage of the first move. In the 1990s, this opening saw a renaissance, and is now seen in the praxis of players from beginner to grandmaster. The Four Knights usually leads to quiet , though there are some variations. The "ECO" codes for the Four Knights Game are C49 (Symmetrical Variation, 4.Bb5 Bb4), C48 (4.Bb5 without 4...Bb4), C47 (4.d4 and others). White's most common move is 4.Bb5, the Spanish Variation. This variation can also be reached from the Ruy Lopez, Berlin Defence. After 4.Bb5, Black has three major alternatives. The first of these is