Marshall Variation

Petrov's Defense

1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 7.O-O O-O 8.c4 c6

Black puts the bishop on d6 and meets White's c4 with ...c6, keeping d5 solid.

The idea

Black develops with 6...Bd6, castles, and answers 8.c4 with 8...c6, holding d5 with a pawn rather than pieces. The bishop on d6 aims at White's kingside.

Wikipedia calls this the Marshall Variation; Lichess's opening names give that name to 6...Bd6 and call the 8...c6 line the Staunton Variation.

Plans for White

Keep the pressure on the center with Re1 and Nc3, and look for cxd5 to open the c-file. White's pieces are slightly more active, and Black's knight on e4 is a target.

Plans for Black

Support the knight on e4 with ...f5 or ...Re8 if needed, and develop the queenside with ...Nd7 or ...Na6. The bishop on d6 and the knight on e4 give Black kingside chances if White is careless.

Watch out for

For White, the kingside. With Black's bishop on d6 aimed at h2, careless moves can allow a bishop sacrifice on h2. Watch the diagonal from d6 to h2.

For Black, the knight on e4. If its support is exchanged away, it can be attacked by Nc3 and Re1 and run out of squares.