What is the epic song of a group?


I will start. I vote for Stairway to Heaven for Zep. Its grand with a great finish. I will throw in Salisbury by Uriah Heap. Ok lets see some posts of what you think is a groups masterpiece.
128x128blueranger
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.....





I'm disappointed to see members mentioning not necessarily the most epic songs by a band, but rather the old, most popular hits that everyone knows by heart.
I must agree with OP concerning Deep Purple and Child in Time. I think that would be their high water mark. Let's see, what else...

Sway - Rolling Stones
November Spawned a Monster - Morrissey 
Accidentally Like a Martyr - Warren Zevon
Precious - The Pretenders
I've Returned - Squeeze
Junkhead - Alice In Chains
Street Life - Roxy Music
It's Over - Level 42
Untogether - Lush
Adam and Eve - October Project

I could think of a million more, but these are the first to come to mind.