Fusing unlikely theatrical elements is stimulating even when unlikely to succeed.

The whacked audacity of, say, Tod Machover's Brain Opera (which attempted to replicate brain functions in music) or Mark Dendy's Dream Analysis (choreographed psychotherapy with appearances by Martha Graham and Judy Garland) take you out of yourself more than things that are tidy and polished.

The Hidden City Festival's Battle Hymns might easily have joined the company of incomplete experimental adventures, with the Mendelssohn Club of Philadelphia singing David Lang's exhausting, unaccompanied choral score and joining the Leah Stein Dance Company in choreographed movements, all amid the questionable acoustics of the Armory of the First Troop Philadelphia City Cavalry.

So many possible pitfalls, however, made the piece's success all the more heroic. Lang's score is a marvel even by his increasingly high standard. Stein's choreography consistently underscored the music's power. The inevitable what-did-it-all-add-up-to question had the right open-ended answers.

The subject was the emotional price of war - explored with only sketchy exterior trappings and suggesting that, whether the cause is worthy or not, wars are conjured by the few at the life-destroying expense of the many. It was about death beyond statistics, each one affecting a network of people among the living. With artists such as Lang and Stein, the potential immediacy of the piece could have been lost in overly refracted abstraction. But those who leave Battle Hymns confused are those who try to figure out surface matters.

The final movement, for example, employs the words to Stephen Foster's "Beautiful Dreamer," but if you expend too much attention hunting for the lyrics (which are used more like a floor plan than in a tune), you'd lose the impact of the singers catching their breath, suggesting hypnotic keening - or death knells.

The five movements had no usual sense of beginning, middle, and end; all were their own worlds with two or three broadly drawn elements in various states of meshing and unmeshing. Overall, Lang's music is minimalist-based, though without the mechanistic smoothness one associates with that type of composition. Lang sometimes seized upon a few key words, repeating them obsessively not just to get every last bit of meaning but to go beyond that. When the second movement zeroed in on the words "tell me," vocal lines led upward and to nowhere, as if asking unanswerable questions.

By conventional standards, each movement was too long; on its own terms, length was justified by the way it occupied your psyche, seemingly in real time, not letting go until your submission was complete. That process doesn't feel great at the time, but you reached the end of each movement feeling changed in indefinable ways.

Much of the piece's heroism had to do with the Mendelssohn Club, heard in the second of the two performances it sang on Saturday. The repetitiveness of Lang's music - often with music director Alan Harler conducting with his ear pressed to an electronic metronome - is affecting for audiences but hugely strenuous for the singers. Even with occasionally ragged moments, I couldn't respect this group enough.