By 1975, Led Zeppelin were the undisputed heavyweight champions of the rock 'n' roll universe. That year, all six of the band’s records had re-entered the charts in the wake of the release of Physical Graffiti, and their tour of North America had been one of the most lucrative of all time. They capped off what had already been a banner year with a career-defining five-night residency at London’s Earls Court Exhibition Centre, begun on May 17, 1975.