What is the epic song of a group?

Traffic - Low Spark of High Heeled Boys
This truly Epic.

For Eric Clapton - I would say Layla even though I personally think Wonderful Tonight (about the same woman) is the better song. It's just not epic.

Hall & Oates - Can't Stop the Music, or 70's Scenario.

When I was a small boy I heard 'River Deep,Mountain High' by Tina Turner for the first time.  The melody of the song made an awesome impression on me and the hairs on my neck literally stood up.  That was a rare experience....

...haven't seen it, and am surprised:

Don't Stop Believen'... - Journey

...don't know if you would consider Peter Gabriel as a group, but if so: 
SLEDGHAMMER!