Back in early March, before we knew not to take such luxuries for granted, a hundred or so music fans walked up the rain-covered steps of All Souls Unitarian Church off 16th Street NW in Washington and took seats in the pews. It was a Sunday night, and the historic sanctuary had been outfitted for acoustics, not worship. Those of us in the audience turned our heads to the rear of the church, where the Barclay Brass, a visionary ensemble borne out of the Washington area’s diverse musical community, had set up in a balcony alcove in front of the pipe organ.

The Barclay Brass is a classical outfit comprising trumpeters, trombonists, French hornists, euphonists and one tubist, co-founder Willie Clark. Imagine all the thunder and authority of classical music, but without balancing strings and woodwinds. It is a rare enough configuration even in the classical world, but the Barclay Brass, which features 11 musicians (the technical term is undecet) rather than a customary single or double quintet, is rarer still. It’s not easy to find almost a dozen orchestra-quality brass players with time for an unpaid exploration of a musical sub-sub-genre. But D.C. has a reserve of classical professionals that few other cities can boast thanks to the National Symphony Orchestra, the Washington National Opera and the U.S. military.

Nearly all Barclay members are active military musicians, including Clark. The membership has rotated since he and trumpeter Nathan Clark (no relation) bonded with trombonist David Miller at a music camp about a decade ago. They started performing in 2015, inspired by decades-old institutions like Empire Brass and the Canadian Brass.

Brass instruments were popularized only in the early 19th century. While unique traditions in this mode have taken root throughout England, the Balkans, New Orleans and the Caribbean, the western classical repertoire remains small. “Comparatively, to a string quartet, we have not much literature at all,” says trumpeter Amy McCabe, the fourth core member of the group. “There’s a lot of room to explore and expand this genre.”

This largely crew-cut and stiff-shouldered group is an odd fit for the contemporary classical world, which has grown highly experimental in terms of tonality, instrumentation and cross-cultural pollination. At the March concert — a celebration of contemporary female composers called the WoCo Fest 2020 featuring several ensembles — the Chicago-based Third Coast Percussion used its boundless collection of bells, mallet keyboards and drums to delirious effect, creating lush soundscapes and pounding repetitions. In comparison, the Barclay Brass’s seated, formal performance might seem tame or old-fashioned.

The group loomed in the mezzanine among the towering and protruding organ pipes, perhaps the appropriate place for metal tubes that sing with air. Miller, who has driven much of the group’s creative expansion, often adapts pipe organ charts for his arrangements. When they began, they summoned the sensation of a religious building literally abuzz with an expertly played organ. We could feel the grand nave’s wood pews vibrating through the cushions beneath us. Whenever the musicians swelled from a whisper to a roar, the air in the building changed.

The source of the roar was Willie Clark’s tuba — nearly the size of a harp and even more formidable. Its rounded lower curve rested in Clark’s lap while he bear-hugged the nickel-plated instrument’s middle and the foot-thick bell horn bloomed above him. The mouthpiece was as wide as a tennis ball. Clark barely moved as he played, just the quick dance of his fingers on the instrument’s three valve keys.

The ensemble’s set was diverse, including a world-premiere composition called “Resolute Fanfare,” as courtly as its title suggests, by guest euphonium player Gail Robertson. As with a choir, there was huge pleasure in being overwhelmed by the magnitude of human breath. When the group occasionally reached a collective rest, we could hear the musicians gasp in unison, preparing themselves for the next plunge. It was a reminder of the mere mortals behind such a supernatural sound.

The Barclay Brass has played almost 30 concerts in five years, a steady clip for an off-hours project, and has found ways to remain active during the pandemic. It frequently shares performances and recordings on its YouTube page, and released its first Zoom video last summer. As of October, the Barclay Brass has begun playing socially distanced outdoor concerts, including events held by the Boulanger Initiative, the organization that sponsored the March concert,and an Oktoberfest at Lutheran Church of the Reformation in Washington. It has also taught a master class for students at the University of Maryland.

Back at All Souls in early March, I asked Miller to account for the ambition of the group. It was two months after the sudden death of Rush drummer Neil Peart, and Miller revealed he was in mourning. “They were the biggest influence on my decision to pursue a career in music,” he told me. “Their music transcends any kind of style or boundaries. They had their own manner.” The Barclay Brass filled the church with its own indefinable power that night, more austere than Rush but no less eccentric or exploratory.

John Lingan is a writer in Rockville.