
Tomorrow marks the 50th anniversary of what many contend is the largest gathering of people in U.S. history.

Summer Jam at Watkins Glen 1973 is also considered to be the largest paid concert ever held, Ticketron sold 150,000 tickets, though eventually it is thought that over 600,000 people made it to the Watkins Glen Grand Prix Raceway to see the triple bill of The Allman Brothers Band, The Band, and The Grateful Dead.
Many of the attendees were already there the day before the concert and watched the soundchecks for each act. The Allman Brothers and the The Band each did a few songs, but the Grateful Dead's idea of a soundcheck turned into a 3-hour long 2-set concert, one full day prior to the official event.
One pioneering aspect of this concert's live sound was the use of several Eventide DDL 1745 digital delay units to sync the sound coming from the PA speakers situated on 4 towers located near the rear of the crowd with the stage sound, solving the problem of equal volume and timing of the sound coming from the front of the stage to the very rear of the crowd. Beyond cutting edge for 1973.
This would be the last concert held at Watkins Glen until Phish did a 3-day festival there in 2011.