The a cappella ensemble Pomerium. (Courtesy of Pomerium)

New York-based a cappella ensemble Pomerium treated Library of Congress visitors Saturday afternoon to a celebratory program of Renaissance music that was as hauntingly emotional in performance as it was cerebral.

With its founder and director, Alexander Blachly, conducting and introducing each work with insightful commentary, the 14 singers demonstrated why Pomerium is considered the consummate U.S. interpreter of early chapel choir music.

In Tomás Luis de Victoria’s hymn “Vexilla Regis Prodeunt,” the six women and eight men showcased an artful blend of voices, alternating between the solemn, resonant chant in the baritones and basses and the tenderly ringing, polyphonic verses in the full ensemble.

For the program’s earliest and sole 15th-century work — the introitus from Johannes Ockeghem’s “Requiem” — the group pared down to nine singers, whose vibrato-free voices paid homage to period style and served to highlight the composition’s harmonic intrigue. In contrast, at full strength, Pomerium’s ebullience and tempered dynamics broke through in full color in two motets by Orlande de Lassus and in the Gloria from Giovanni Pierluigi da Palestrina’s “Missa Sine Nomine.” The group’s joyful singing and shapely phrases also had great effect in a motet by Giovanni Gabrieli and in a motet penned by his uncle, Andrea.

The program featured five selections by Josquin des Prez, whose writing illuminated Pomerium’s hallmark ability to sing with a sonorous simplicity that belies a work’s complexity. By concert’s end, the group had fully tamed the Coolidge Auditorium’s dry acoustics with a full and triumphant sound.

Jean is a freelance writer.