BRAINTREE -- To Vito Nicastro, it's one of the wonders of the modern age.

For the vast majority of Catholic history, he said, you'd have to go halfway around the world to hear a Mass in Ukrainian. Nowadays, all you have to do is take the T to Jamaica Plain and visit Christ the King Ukrainian Catholic Church.

"We can experience their history alive," said Nicastro, associate director of the Archdiocese of Boston's Office for Ecumenical and Interreligious Affairs. "It isn't just in the books. It's happening."

The Ukrainian Catholic Church is one of eight Eastern Catholic churches with a presence in the archdiocese. There are 23 self-governing Eastern Churches worldwide. Each has its own history, liturgy, and cultural traditions, but all are in communion with Rome and governed by the pope.

"The whole Catholic Church is made up of those of us who are united in the Holy Spirit by the same faith, the same sacraments, and the same governance, namely the Holy Father in Rome," Nicastro said.

The terms "rite" and "church" are often used interchangeably, Nicastro said, but while each of the Eastern Catholic churches has its own rite (or liturgy), they are all part of the universal Catholic Church. The Archdiocese of Boston is a Latin Rite archdiocese. Nicastro said that many Catholics don't realize that their liturgy is only one of many rites.

"They all come from a unique place with a unique culture, so it's very important to understand their individuality," he said. "And that is the beauty of them."

The Eastern Catholic churches came about due to the travels of the apostles and their subsequent followers. When they established churches in the East, those churches conformed the faith to their own history and culture. After the Great Schism, the Catholic Church tried and failed to restore communion with the Orthodox Churches throughout the Middle Ages. When these attempts fell through, Rome sent missionaries to the East, who persuaded some Orthodox Christians to enter communion with Rome. Most Eastern Catholic churches have an Orthodox counterpart. The Eastern Catholic churches are often confused with Orthodoxy due to their similar art, architecture, and use of icons in prayer. Other Eastern Churches, such as the Maronites, have always been in full communion with Rome and therefore have no Orthodox equivalent.

"It shows the beauty of the universal faith because it can be interpreted and translated into not just languages, but the ways of life that these churches have built over many centuries," Nicastro said.

The Second Vatican Council produced an entire document about the Eastern Catholic churches. Entitled "Orientalium Ecclesiarum" ("On the Eastern Churches"), it reaffirmed those churches' right to maintain their self-government and traditions. Some Eastern churches allow clergy to marry and Eastern Catholic prelates can be made cardinals and vote in papal conclaves.

"The document makes a very strong point that these churches are to be respected and honored and venerated for holding fast to the traditions that were given to them by the Apostles," Nicastro said. "That they are to be accorded the fullest respect and considered equal with the Latin Church, the Latin Rite."

"Orientalium Ecclesiarum" also states that every Catholic should be taught about rites different from his or her own.

"I think that's important because there are so many riches spiritually that we can learn from our Eastern Catholic brothers and sisters," Nicastro said.

The history of the Eastern Catholic churches in Greater Boston, he said, is the history of immigration to the area. The territory of the Archdiocese of Boston is home to Melkite, Armenian, Maronite, Romanian, Syro-Malabar, and Ukrainian Catholic churches, established by immigrants from Eastern Europe, the Middle East, and India. The Melkite Catholic Eparchy of Newton's territory overlaps with the Archdiocese of Boston. Other Eastern Churches have communities in Latin Rite parishes. The Cathedral of the Holy Cross in Boston holds Sunday Mass in the Ge'ez Rite of the Ethiopian and Eritrean Catholic Churches. Mary Immaculate of Lourdes Parish holds occasional Masses in the Chaldean Rite.

"They have a great deal to teach us about longevity in the faith," Nicastro said. "If you're a Christian from Syria, or Iraq, or Egypt, or Armenia, you know something about holding onto the faith in difficult circumstances and sustaining that, lasting through years, generations, centuries."

Modern life in the U.S. is so transient, he said, that it's difficult to comprehend a single family attending the same church for the better part of a millennium.

"We have a lot to learn from their spirituality, but also their enduring witness," he said. "The Armenians survived a genocide. The Armenians are still witnessing to their faith in Christ after a genocide."

Nicastro called the Eastern Churches "treasures" of the Catholic faith.

"They really are the family jewels," he said. "This is the treasure of the Catholic Church. The learning, the piety, the spirituality that all of these Eastern Christians developed over the centuries and live in our midst today."