The Four Knights was one of the workhorses in the family of the Open Game, at even the highest levels, until World War I.

In this period ambitious players explored the Ruy Lopez, believing it a better attempt by White to exploit the advantage of the first move.

This variation was played in the fifth game of the 1996 Deep Blue versus Garry Kasparov match.

The line is a favourite among younger players due to its simple and easy development but was also used successfully by Nigel Short against Antoaneta Stefanova.

After 5...Kxf7 6.Nxe4 d5 7.Neg5+ Kg8, Black is already threatening 8...e4, and after 8.d3 h6 9.Nh3 Bg4, Black has a very powerful position, with an unopposed light-squared bishop, a strong duo of pawns in the centre, and a safe king, while White needs to work out how to get the displaced knight on h3 into play; often it will need to be played back to g1.

?, as in a match game between Siegbert Tarrasch and Emanuel Lasker in 1916, which led to a Black win in 23 moves.

A Halloween Gambit style 4...Nxe4 has also been tried at the grandmaster level as in two games between Ilya Smirin and Bartłomiej Macieja.

The quiet waiting move 4.a3, the Gunsberg Variation, is a specialty of Polish grandmaster Paweł Blehm.

After 4...Nxe5 5.d4, White tries to seize the centre with his pawns and drive the black knights back to their home squares.