When Janet Cardiff’s “Forty-Part Motet” went on view at MoMA PS1 in the weeks following the September 11 attacks in 2001, its joining of collective song and individual voice summoned for many visitors 9/11’s distinctive combination of national tragedy and personal loss. Today, we remember.

*If you missed the Forty-Part Motet at MoMA PS1, or if you can’t get enough (like us), it’s currently on view at The Cloisters.