Why is 4...e5 not popular in the Smith-Morra Gambit? When I encounter the Sicilian as White, I often will play the Smith-Morra Gambit.  My opponent played 4...e5, but this does not appear to be a very popular move as there are only 2 games on www.chessgames.com that have it, one of them being here, which is apparently the first ever Smith-Morra Gambit recorded.  I didn't even see Wikipedia give it as an option, so I was curious to know why 4...e5 is not popular or in other words, what drawbacks does it have?

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1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5
Simply stated, it's because of Black's backward d-pawn; see http://en.wikipedia.org/wiki/Backward_pawn -- as opposed to other lines of this Gambit it gives White a definite weakness to focus on well through the opening and possibly the middle-game and beyond.