CAMBRIDGE -- The undulating, ethereal vocalizations of a choir of men chanting melodies in Greek seem to transcend space and time, sweeping back the veil separating Heaven and Earth.

It could have been a scene straight from a medieval monastery -- if not for the iPad one of the singers was using to read the music.

The St. Romanos the Melodist Byzantine Choir of the Hellenic College of the Holy Cross joined the choir of St. Paul Parish in Harvard Square on Nov. 9 for "Credo," an ecumenical concert celebrating the 1700th anniversary of the Council of Nicaea.

During the Council of Nicaea, the church's first ecumenical council, held at a time before there was a division between Catholic and Orthodox, bishops gathered to define the fundamental tenets of faith and establish a common date of Easter for all Christians.

"Our God is a god of unity," said Father Romanos Karanos, director of the Byzantine Choir. "There are a lot of things that divide humanity. Unfortunately, the Western and Eastern churches have been split for almost 1,000 years now, and we need to find the common ground, the common artistic, musical, liturgical tradition that unites us, so that hopefully at one point we will reunite."

Metropolitan Methodios of the Greek Orthodox Metropolis of Boston attended the concert, which was hosted by the Harvard Catholic Forum. Forum Executive Director Deacon Tim O'Donnell wanted the concert to show the timeless traditions of Eastern Orthodox music and the way that Catholic music has evolved over the centuries.

"We have the Eucharist in common," he said. "We have music in common. We do music differently, but we have it in common. So it's an opportunity to come together."

The musical selections followed the structure of the Catholic Mass and Eastern Orthodox Divine Liturgy. It began with Kyries performed by both choirs, then the singing of Psalm 50 in English and Greek. St. Paul's Choir sang Vivaldi's "Gloria," and the Byzantine Choir sang the "Trisagio Eastern'' Christian hymn dedicated to the Holy Trinity. The Byzantine Choir recited the Gospel in Greek and sang the Cherubic Hymn. St. Paul's Choir sang Stravinsky's ''Ave Maria" and Haydn's ''Sanctus,'' the Byzantine Choir sang ''Hagios,'' the Orthodox equivalent. For the majority of the concert, the Byzantine Choir was in front of the altar while St. Paul's Choir was in the choir loft. Father Karanos said this was done to reflect the ancient antiphonal tradition, where one choir responds to another.

"It was magnificent," he said. "The acoustics are amazing, and I could feel the spirituality of the people in the audience."

The two choirs united for a singing of the Catholic hymn "Ubi caritas" and the Orthodox hymn "O Pure Virgin," composed by St. Nectarios.

St. Paul's Choir Director Nara Lee had never heard Eastern Orthodox liturgical music in person before the concert.

"We sing the same text, but in very different styles," he said. "So it's amazing we can hear all different styles in one place."

In his two years with St. Paul's Choir, Lansing Horan had never heard anything like it.

"I don't really have the occasion to come across a lot of Byzantine-style music," said Horan, a PhD student in nuclear engineering and plasma physics at MIT. "And being able to have our two choirs alternate back and forth, it was just awesome."

He's used to singing Gregorian chant, but not as familiar with Byzantine hymns.

"I really like the fullness of the sound, from the drones that they incorporate, and how it fills the space," he said.

Byzantine Choir member Nicholas Ververis, a seminarian at Holy Cross, said that the concert was a "blessing," especially because he has Catholics and Orthodox Christians in his family.

"I grew up in the church, so it's really something that helps our worship, and it really touches the soul differently, and touches the heart," he said.