Morphy Defense, Caro Variation

The Caro Variation, 4...b5, settles the question of the Spanish bishop immediately. Black removes any later Bxc6 and so makes e5 permanently secure. The early timing is unusual because e5 does not yet need help: after 4...Nf6 5. Bxc6 dxc6 6. Nxe5 Qd4 Black regains the pawn with a fork. White's reply 5. Bb3 is played almost without exception. The bishop goes to the a2-g8 diagonal with a free tempo and aims at f7. The line takes its name from Horatio Caro, who adopted it in the 1880s, although Charles Henry Stanley had already used it against Eugène Rousseau in 1845.

After 5. Bb3, Black can choose between four main ideas. 5...Na5, the Norwegian Variation, hunts the bishop and was associated with Svein Johannessen and Mark Taimanov. 5...Bb7 was Caro's own choice, often combined with a double fianchetto, and it frequently transposes into the Arkhangelsk once White castles and Black plays ...Nf6. 5...Bc5 is the Graz Variation, which became popular only in the 1990s. 5...Nf6 heads for the main lines but allows White to answer with d4. Engines rate the position as roughly balanced, and White scores better in online play.