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But it wasn’t the historic nature that captured the sold-out audience’s attention.

It was the way these two groups came together seamlessly to create classical music’s version of a rock supergroup.

Vocalists from the state’s Grammy-honored Phoenix Chorale and ÃÛèÖÖ±²¥â€™s putting aside any ÃÛèÖÖ±²¥-Phoenix/ASU-UA rivalries for a joint concert might have seemed unthinkable not too long ago.

But here they were, on ÃÛèÖÖ±²¥â€™s Catalina United Methodist Church stage on Friday, Oct. 11, flanked by towering chrome pipes from the church’s magnificent Quimby organ, singing Frank Martin’s unaccompanied Mass for Double Choir.

Under the baton of True Concord Music Director Eric Holtan, those 48 vocalists — 24 from each ensemble — let their voices soar in the Kyrie and the audience filling nearly every seat in the sanctuary and the loft was wrapped by a wall of amazing sound.

This was more than singing; those voices created a symphony, with lush melodies coming off like a magnificent string section. Tenor and soprano voices hit breathtakingly impossible high notes like lush violins, balanced by the soaring lyricism from the midrange that sat in for cellos and violas. A singular bass voice resonated like a tuba, rich and powerful, in the Gloria. Wonderful two-part harmonies alternating between the tenors and sopranos, baritones and mezzos and bass and altos punctuated the prolonged Credo.

Everything about this piece was brilliant.

The last time True Concord performed Martin’s Mass was in 2013 with the University of ÃÛèÖÖ±²¥â€™s ÃÛèÖÖ±²¥ Choir. It is not a work that is programmed often given the need for double choir, and to hear it performed by these two great professional ensembles felt like a once-in-a-lifetime moment.

Artistic Director Christopher Gabbitas, who has been at the Phoenix podium for five years, led the combined ensembles in the second-half performance of Maurice Duruflé’s Requiem, accompanied by the incredible organist Jeremy Filsell playing Catalina Methodist’s Quimby.

Daruflé borrowed Gregorian chants for the organ suite, but at times the music sounded like it also borrowed from Hollywood’s deep vault of early horror flicks — the black-and-white silent films accompanied by live organ. Near eerie interludes led to more contemporary melodies. When Filsell struck those low moaning notes in the “Domine Jesu Christe� third movement, the choir erupted in an exclamation. Uptempo passages made way for slight dissonance reminiscent of a great rock opera.

The wonderfully voiced baritone Edward Vogel, a relative newcomer to True Concord, soloed in the movement; longtime Phoenix Chorale mezzo-soprano Holly Sheppard was the soloist for the “Pie Jesu� movement, accompanied by cellist Jay Good. The combination of organ, cello and Sheppard’s serene mezzo was sublime.

The concert closed with the solemnity of Fauré’s “Cantique de Jean Racine,� a short but extraordinarily beautiful work that we quietly wished was a little longer. That would have given us a few more minutes to appreciate the scope of what we were experiencing and hope that this was the first of many collaborations to come.

True Concord and Phoenix Chorale were set to repeat the concert at Catalina United Methodist, 2700 E. Speedway, at 7 p.m. Saturday, Oct. 12, before taking the show to Phoenix on Sunday, Oct. 13, for a 3 p.m. performance at Camelback Bible Church, 3900 E. Stanford Drive in Paradise Valley. That concert is sold out.