Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1/6...b5/7. Bb3/7...d6/8. c3

=Ruy Lopez Main Line=

With White preparing to strike in the centre with d4, Black's king typically vacates the premises with 8...O-O. The old-fashioned move is 8...Na5, which may transpose, but the loss of control over d4 may allow White to save a tempo by omitting h3.

8...Bg4 is seen from time to time, discouraging an instant d4 by White. White will probably play d3 as a temporary measure, aiming to bring the queens knight to the kingside to evict the bishop in order to achieve d4.