In the early 16th century, groups of European Christians started splitting from the Roman Catholic Church in what is now known as the Protestant Reformation. But while Protestants and Catholics were at odds, they had one thing in common: Anabaptism had to be eliminated.

The Reformed Christians drowned Felix Manz, the first of thousands of Anabaptists martyred over the next two centuries. The Catholics burned at the stake Michael Sattler, author of the first Anabaptist confession of faith. Even Martin Luther, who is credited with ushering in the Reformation, urged the execution of all Anabaptists as heretics.

Such persecution helped drive the early Anabaptists -- the spiritual ancestors of today's Mennonites, Amish and Hutterites -- into isolation, suspicious of the rest of the world.

But now, nearly 500 years later, Catholic, Lutheran and Reformed churches -- the primary antagonists of Anabaptists in the 16th and 17th centuries -- are seeking to make amends.

"We all have black sheep in the family. We all have ancestors that we aren't proud of," said Bishop Joseph F. Martino, head of a Vatican-appointed delegation that last fall concluded five years of meetings with a group from the Mennonite World Conference, the global Mennonite fellowship.

In addition, the Evangelical Lutheran Church in America and Mennonite Church USA finished a two-year series of meetings this spring. And on June 26, the Reformed Church in Zurich, Switzerland, will hold a reconciliation ceremony with participation by Anabaptist descendants from around the world.

More than 2 million Anabaptists live in 60 countries, according to the Center for the Study of Global Christianity in South Hamilton, Mass. About 615,000 live in the United States, with the greatest concentrations in Pennsylvania, Indiana and Ohio.

The Protestant Reformation was born in 1517 when Luther, a Catholic monk, challenged the church by posting his 95 theses in Wittenberg in what is now Germany. He went on to found the Lutheran Church. Another pivotal development came in the early 1520s when Ulrich Zwingli, a priest, renounced Catholicism but remained in the pulpit of Zurich's main church, giving rise to the Reformed movement.

But some Christians thought Luther, Zwingli and other reformers did not go far enough. Particularly at issue was infant baptism. For generations, newborns had been baptized, but some believers argued that only adults are capable of making a decision to follow Jesus and join the church.

Leaders of the growing movement insisted on the rebaptism of adult believers -- the first adult baptism was conducted in Zurich in 1525 -- and refused to have their children baptized as babies. Adherents eventually adopted the derogatory name used by their critics: "anabaptist," meaning rebaptized.

The dispute was not only religious, but political. Baptism was a formal entry not only into the church but also into citizenship in the state. State and church were one, whether Catholic, Lutheran or Reformed, and rejecting infant baptism -- the accepted practice since the 4th century -- was seen as threatening the civil order.

As a result, Anabaptists were severely persecuted. Thousands were drowned, beheaded or burned at the stake. Others fled across Europe and eventually to the Americas in search of security to practice their faith.

Many Lutherans are unaware of that chapter of their church's history, said Paul Schreck, associate for bilateral dialogue of the Evangelical Lutheran Church in America.

"I think most Lutherans around the world would be horrified that their forebears put to the sword people who disagreed with them," he said.

Both the Catholic and Lutheran dialogues with Anabaptist groups covered many topics, but they included repentance. In the final report of the Catholic-Mennonite meetings, released this spring, the Vatican delegation said Catholics "can express a penitential spirit, asking forgiveness for any sins which were committed against Mennonites, asking God's mercy for that, and God's blessing for a new relationship with Mennonites today."

After their meetings with the Mennonite Church USA, Lutheran participants released a statement repudiating state-sanctioned persecution of Anabaptists by their church.

Starting next year, the conversation will go global, as the Mennonite World Conference and the Lutheran World Federation will start meeting together. One of the items on the agenda is the Augsburg Confession, the Lutheran statement of faith, which was written in 1530 and includes condemnations of Anabaptists.

The study of history was an important element of both the Catholic and Lutheran dialogues. Martino said it is important for all sides to have a common understanding of the past.

"A lot of time people have strong feelings based on certain things they regard as gospel truth," said Martino, the Roman Catholic bishop of Scranton, Pa. "Once the playing field is leveled, then you get into a position where you can talk on a secure foundation. The perceptions and the judgments are adjusted."

That applies to Anabaptist history as well as Catholic and Lutheran history. The martyr heritage has been crucial to the Mennonite, Amish and Hutterite identity.

Important to those groups is "Martyrs Mirror," a 17th-century book of 1,290 pages with hundreds of accounts of persecuted Anabaptists. But that heritage may need reexamination, said Larry Miller, Mennonite Conference executive secretary, not to "betray the blood of the martyrs" but to be sure the stories are accurate and convey the radical nature of Anabaptist belief.

"We like to say we were just being obedient" to biblical mandates, Miller said. "But if you take a look at it from another angle, you can say we were socially provocative."

The World Alliance of Reformed Churches, which includes Presbyterians and Congregationalists, apologized more than 20 years ago. But next week's event in Zurich is different, because of that city's prominent role in the mistreatment of Anabaptists, said John Sharp, director of the Mennonite Church USA Historical Committee.

Evangelical-Reformed Church in Zurich is taking responsibility for what happened in its territory centuries ago.

"This is the canton [jurisdiction] that did the first executions," said Sharp, who will lead a delegation of about 80 U.S. and Canadian Mennonites and Amish to the event. "This is the canton that did the persecution. This is the canton that was intolerant."

The Zurich ceremony, commemorating the 500th anniversary of the birth of Reformed leader Heinrich Bullinger, will include a joint worship service and the dedication of a memorial to Manz, who was drowned in the city's Limmat River in 1527.

The commemoration "is not something we wanted or needed or expected," Sharp said.

"We should acknowledge it with grace and understanding as part of an ecumenical impulse toward dialogue."

Staff writer Bill Broadway contributed to this report.

An etching from the 17th-century book "Martyrs Mirror" shows two Anabaptists, Levina and David, being executed in Ghent, Belgium, in 1554. Another "Martyrs Mirror" etching shows two women being led to their deaths in Bamberg, Germany, about 1550. Felix Manz, the first Anabaptist martyr (as imagined and painted by Tom Schenk in 1972) was drowned in Zurich in 1527.