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 careful play White is held to gain an advantage. The best moves are 4.Nxd4 exd4 5.O-O Bc5 6.d3 c6 7.Ba4 Ne7. This defence was published in 1843 in Paul Rudolf von Bilguer's "Handbuch des Schachspiels" and explored by Henry Bird in the late 19th century. Bird played it as Black at least 25 times, scoring +9 =3 −13 (nine wins, three draws, thirteen losses). Bird's Defence was later used a few times in tournament play by Siegbert Tarrasch, Boris Spassky, and Alexander Khalifman. Although it is still sometimes seen as a surprise weapon, no strong master since Bird has adopted