Debate: Who are the 'big four' of classic rock?

The names of the bands that comprise the 'big four' of thrash metal are almost universally accepted: Metallica. Megadeth. Slayer. Anthrax. Easy.

Widen the scope to other eras and genres, and it gets complicated, particularly where it comes to classic rock. How do you carve a new Mount Rushmore when it's so difficult to define what's being celebrated? What is classic rock?

Is it an era? The programmers of classic rock radio stations in the US would like you to think so, although, as time passes, their remit has expanded to include artists who weren't around during rock's 70s heyday but whose sound fits the format.

Is it a sound? If Led Zeppelin are the archetypal classic rock band, does their blues-driven sound provide a template, or is that too narrow? Where does that leave Pink Floyd or Genesis? Black Sabbath? Motörhead? Does progressive rock join the club? Does heavy metal?

Is it about influence? No single moment inspired more rock musicians to pick up a guitar than the Beatles' appearance on the Ed Sullivan Show, and their later albums created a blueprint for rock to follow. Still, many would baulk at their inclusion in a list of great rock bands, sniffily confining them to the world of pop.

Perhaps, in the end, it's purely a personal choice. We all have our own definitions, and we all have our own favourites.

So what's your pick? How do you define classic rock, and who would be in your personal 'big four'?

Let us know in the comments below.