What is the epic song of a group?

It isn't their best or most memorable song maybe 'epic' isn't the right catagory perhaps song that redefined a group or introduced something new. The wiki page on the song  is an interesting read. 

OK what about The Rolling Stones and Goin' home from Aftermath UK version of course

Ten Years After’s I’m Going Home at Woodstock is even more epic coming in at 11:24 on Youtube. Maybe the most epic of them all. Excellent sound quality. Headphones are recommended.

https://youtu.be/bW5M5xljdCI

My personal Musings on the subject.....
+1 for Genesis, Suppers ReadyProcol Harum, Whiter shade of PaleSmall Faces, Itchykoo ParkThe Rolling Stones, Finger Print FilePatti Smith Group, WaveTodd Rundgren, Parallel LinesPink Floyd......Ok, everything they did.Traffic, Dear Mr. Fantasy (I know some will argue Low Spark but I dig Mr. Fantasy)Adrian Belew, I am what I amKing Crimson.....(Ok, lets not even go there at trying to guess.)Yes, "Siberian KhatruNeil Young, Old Man or A Man Needs a Maid or Cortez.....you pick.Andrew Newton, His version of Hallelujah (best I ever heard anywhere by anyone. Ever!)Genesis, Seven Stones.....wait, I already chose....Van Morrison......(all he has to do is open his mouth and it’s epic)Mark Knopfler, (see Van Morrison above but add guitar)Santana, Soul Sacrifice Live at Woodstock https://www.youtube.com/watch?v=AqZceAQSJvc
Speaking of Woodstock: Joni Mitchell, Woodstock performed live, what a voice! https://www.youtube.com/watch?v=3aOGnVKWbwcSpeaking of voices, the woman with the four octave voice.....Phoebe Snow, https://www.youtube.com/watch?v=7OxTVxGhHFMAllman Brothers Band, Melissa.....love this acoustic version https://www.youtube.com/watch?v=ggeab0lKz2c
Natalie Merchant, Um, well, if I had to choose then (hand over my eyes) Gulf of ArabyTori Amos, IciclesELO, Can’t get it out of my HeadThe Band, of course, The Weightetc.....etc.....etc.....

Drat! Can't get this to save as a list.