It's one of the eternal questions argued by classic rock aficionados — which of these virtuoso bands could rock the hardest? Perhaps the only people qualified to make that call were those lucky enough to be at Merriweather Post Pavilion in Columbia, Md. on the night of Sunday, May 25, 1969, when Led Zeppelin opened for The Who in one of the most epic double bills in rock history. It was a pairing of hall of fame live acts that would never be seen again on the same stage.
