In Phil Ball's book on Spanish football, he says that, between Barcelona and Real Madrid, there is "so much morbo you would have to employ a very powerful priest to exorcise the phenomenon."
However, he can't quite put his finger on how to describe what is known in Spain as "morbo"—though you can probably imagine it has a fair amount to do with the intensity that surrounds the rivalry.
With that intensity in mind, it's not hard to understand why there have been so many thunderous editions of El Clasico through the years.
And, rather than improving over time, the relationship between the two clubs has worsened, as they have become more dominant than ever in the 21st century—leading to more frequent and more fierce versions of El Clasico.
Rewinding back over the years, though, here are 10 of the greatest moments from one of the world's greatest fixtures.