One of Black's more aggressive alternatives is the Marshall Attack: after 3...a6 4.Ba4 Nf6 5.0-0 Be7 6.Re1 b5 7.Bb3 0-0 8.c3 Black plays the gambit 8...d5, sacrificing a pawn. The main line begins with 9.exd5 Nxd5 (9...e4?!, the Herman Steiner variation, is considered weaker) 10.Nxe5 Nxe5 11.Rxe5 c6 (Marshall's original moves, 11...Nf6, and 11...Bb7 are considered inferior, but have also yielded good results at top levels of play for Black. GM Joel Benjamin suggests that 11...Bb7 is inferior due to 12.Qf3). The resulting position is shown in the diagram. To the casual observer it might seem that Black has been careless and lost a pawn; however, the sacrifice has also stripped White's of its defenders, given Black a lead in development, and rendered White's 8.c3 irrelevant. Since Black's compensation is based on rather than considerations, it is difficult or perhaps impossible to find a refutation. Black generally goes all-in with a massive kingside attack, which has been analysed to great depth (sometimes beyond move 30) with no definite conclusion as to the Marshall's soundness. The Marshall Attack is a very sharp opening system in which a great amount of theoretical knowledge is vital, and many White players, including Garry Kasparov, avoid it by playing one of the anti-Marshall systems, 8.d4, 8.a4 or 8.h3 instead of 8.c3.