Four centuries later, Easter's date remains divisive. Some church leaders want that to change

ATHENS, Greece — For more than 400 years, Catholic and Orthodox churches have used different ways to determine the date of Easter. But this Sunday will mark a special moment for Christians, as the churches celebrate of Jesus' resurrection on the same day.

What's more, top religious leaders — including Pope Francis — are expressing a desire to keep it that way. But the unusual alignment has stirred underlying mistrust between the two major Christian communions.

Calendars and calculations differ

The movable date for Easter follows a seemingly straightforward rule: the Sunday following the first full moon on or after the spring equinox. But the two churches started using different calendars after Pope Gregory XIII's adaptation in 1582, when the Western church adopted the Gregorian calendar while the Eastern Orthodox Church kept the older Julian one.

Moreover, each church uses its own ecclesiastical calculations for lunar cycles and the equinox, which don't neatly match scientific projections.

The result is that Easter dates can be as much as five weeks apart. They can coincide in back-to-back years, or a decade can pass without it happening.

Pope Francis' wish

Days before his five-week hospitalization, Pope Francis referred to this year's Easter celebration while invoking the 1,700th anniversary of the historic Council of Nicaea, when Christian leaders gathered to settle foundational disputes about the faith.

"Once again, I renew my appeal: Let this coincidence serve as a sign — a call to all Christians to take a decisive step toward unity around a common date for Easter,'' Francis said while leading prayers at the Basilica of St. Paul in Rome.

Francis' invitation, delivered at the end of a prayer for Christian Unity with Orthodox priests present, wasn't new. Returning from a trip to Turkey in 2014, he told reporters on the plane that a unified date would be logical.

''It is a bit ridiculous,'' he said, then staged a pretend conversation: ''‘Tell me, your Christ, when is he resurrected? Next week? Mine was resurrected last week.'''

He has found an ally in Ecumenical Patriarch Bartholomew, a fellow octogenarian and spiritual leader of the world's Orthodox Christians. The two ''speak to one another like brothers,'' Francis has said. For his part, Bartholomew has called Francis ''our elder brother'' and described the Easter initiative as ''a real step toward repairing old conflicts.''

Only winners, no losers?

The idea of a common Easter has been discussed since the 1960s, with interest often peaking when celebrations coincide. The key obstacle has always been the implication that one side would need to concede.

Protestants, who follow the same calendar as Catholics, have also been in on the discussions.

The Geneva-based World Council of Churches — a fellowship of Orthodox and Protestant bodies — has proposed a compromise. It suggests using modern astronomy, basing the calculation on Jerusalem time and following the same basic rule set centuries ago.

''It has never been more important than now, because we live in a polarized world and people all over the world yearn for more unity,'' Lutheran Bishop Heinrich Bedford-Strohm, a senior WCC official, told The Associated Press from his home outside Berlin. ''All other questions – on calendar, on time, on the moon and the stars and everything – it's not primary; it's secondary."

‘Strings attached'

While the pope's wishes may carry powerful influence through the Vatican's highly centralized authority, Bartholomew's role is largely symbolic over the self-governed national and local churches. And discussions between Russia, the Orthodox world's most populous country, and churches of other Orthodox-majority countries remain stalled due to the war and church divisions in Ukraine.

Further complicating prospects for consensus is a history characterized by centuries of mistrust, largely driven by wariness in the East about the Vatican's supremacy.

At a Holy Week service Monday in Athens, Father Anastasios welcomed parishioners into the Church of Saint Dimitrios Loumbardiaris, a restored stone chapel near the Acropolis. He said he supports forging bonds with Christianity's other branches — but with caution.

''We can try to build bridges, but we cannot distort our faith or the traditions of our ancestors, or the dogmas Christ himself handed down," he said. "There are deeply rooted differences. From my view and that of many people here, the unity sought in the past by the Roman Catholic Church often wasn't sincere; it came with strings attached, was more about dominance than genuine reconciliation.''

‘Great harmony'

As dialogue between the churches slowly unfolds, common Easter celebrations are already a practical reality in a few places. The Orthodox Church in Finland switched dates in the 1920s to align celebrations with the Lutheran majority. And Catholics in Greece — while making no official change to their calendar — have celebrated with the rest of the country since 1970.

Joseph Roussos, a member of a Catholic community on the Greek island of Syros, took his first trip to the Vatican last month.

At age 67, he remembers when Easters in Greece were separate: when schools and shopkeepers on the island closed for different holidays, and the church bells tolled mournfully during two distinct Holy Weeks.

''It wasn't a good situation. But when we did celebrate Easter together, there was great harmony,'' he said. ''We live very well (today), and it's truly beautiful. I hope it stays that way.''

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Barry reported from Rome. AP journalist Nicole Winfield in Rome contributed to this report.