I guess you mean the use of strings. As far as classic rock goes, Days of Future Passed by the Moody Blues is a great one, and in newer stuff, Beck often makes good use of strings on some songs. (Morning Phase)
Orchestrated Rock...Uriah Heep and others
https://www.youtube.com/watch?v=zau-okpFssg
Released in 1971 Salisbury by Uriah Heep was always one of my favorite Prog Rock albums and groups.
I recently re-listened to the re-mastered title track on my high end system for the first time. Kind of blew my mind. 16 minutes long.
I concluded that I’ve always enjoyed orchestrated rock, which probalby started with Neal Young’s Harvest.
Any suggestions of other classic rock groups that used orchestration would be appreciated.