Ruy Lopez: Berlin Defense: Repertoire Preparation
Berlin defense is very famous, and the most popular 3rd move alternative to ...a6, even though it occurs one tenth as frequently as ...a6.
The two model games for us are more than a century apart, and both feature a world champion.
First one is Steinitz - Zukertort.
Second one is Carlsen - Anand. Carlsen missed a win many times.