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
Ruy Lopez his 1992 match against Anatoly Karpov and won both games. By playing 6.d3 White steers clear of the Marshall Attack and any of the Anti-Marshall lines. White threatens 7.Bxc6 winning the e5-pawn leaving Black a choice of either 6...d6 or 6...b5. After 6...d6 the e5-pawn is firmly defended and Black threatens to trade off White's Ruy Lopez bishop with 7...b5 and 8...Na5. White normally continues with 7.c3 and after 8...0-0 White can choose between 9.Nbd2 or 9 Re1. Black can also play 6...b5 and after 7.Bb3 d6 (7...0-0 is a viable alternative) White has to deal with the threat of