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 e5 and placing the queen on the c-file which may later become open after ...cxd4. Other Black moves in this position are 11...Bb7 and 11...Nd7; the latter was adopted by Keres a few times in the 1960s. The Chigorin Variation has declined in popularity because Black must spend some time bringing his offside knight on a5 back into the game. The Chigorin is divided into four "ECO" classifications. In C96, Black or White deviate after 10.Bc2, and do not reach the classical main line position 10...c5 11.d4 Qc7. In C97, White proceeds from the diagram with 12.a4, 12.d5, 12.b4, or