Ruy Lopez: Berlin Defense, Improved Steinitz Defense

The Ruy Lopez: Berlin Defense, Improved Steinitz Defense is a chess opening classified under ECO code C66 in the Open Games & French Defense family, beginning with 1.e4 e5 or 1.e4 e6, including the Italian Game, Ruy Lopez, and French Defense. It is reached after 4 moves: 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O d6. The resulting position leaves white to move.