Image: Steve Eck

Capella Romana performs in London’s St. Paul’s Cathedral at the 2004 Byzantine Festival.

WITH YOUR EYES CLOSED, YOU CAN ALMOST FEEL IT. The blood. The flames. The screaming. The brittle thwack of arrows against fortress walls; the wet thunk of another sharpened point finding its mark. It is the spring of 1453, and Constantinople, once the glittering capitol of the Byzantine Empire, is under siege by 80,000 Ottoman Turks.

In less than two months, the city will fall, rocking the foundation of Christendom. But as you envision the besieged metropolis, the church where voices are crying out for deliverance, you hear an altogether more ethereal sound: the harmonic trill of unaccompanied song.

Open your eyes. You’re in Portland. It’s winter. And inside the stained glass of St. Mary’s Cathedral, Cappella Romana, the world’s preeminent early-music vocal group, is giving flight to a program of ecstatic verses and Byzantine chants—just the sort that would have filled a battered church as Constantinople fell in the 15th century. Twelve men are dressed in black, their throats shaping notes with more nuances than a fine wine: the dusky warble from a Middle Eastern sacred chant, the singsong lilt of East India, the guttural brogue of the Slavic tongue, and the hushed monotones of a European monastery. As these finely tuned intersections of culture and language from Constantinople, one of the world’s great crossroads, wash through the room, they inspire a collective act of imagination from the audience. All eyes are closed.

“They don’t want to see the modern Catholic church they’re sitting in,” says Mark Powell, the executive director of Portland-based Cappella Romana and one of its principal singers. “They want to be transported. Our music has the power to do that.”

No other vocal group in the world has managed to perform, perfect, and popularize medieval music quite like Cappella has. It is the time-traveling DeLorean of the vocal world, able to effortlessly switch styles and centuries: from standard choral literature to the full-throated, nasally resonant stylings of the Mediterranean, to dauntingly virtuosic Western music fraught with polyphonic lines, counterpoints, and competing melodies. Other groups can do one thing well; only Cappella spans the gamut. “Our flexibility distinguishes us,” says Powell, whose group will delve into Eastern Europe this month with a performance of Serbian hymns at St. Mary’s Cathedral on February 12. “It’s our ability to switch back and forth while showing the common thread of musical and vocal tradition that extends along Western European and Slavic lines.”