Packing a conference hall in Athens' War Museum, the demonstrators attended a rally organized by a group of theologians and backed by Greece's clerical union - which represents the country's parish priests.
``We applaud the dynamism of this event,'' said the Rev. Dimitris Theopoulos, a union representative. ``We appeal for the archbishop to change his position.''
Archbishop Christodoulos and the Holy Synod, the church's governing body, have come under growing criticism and pressure from priests, monks, nuns and church groups to revoke a decision they took in early March to lift their objections to a papal visit.
More than 97 percent of the Greek native-born population is baptized into the Orthodox Church, the official state religion.
``They invited him without the permission of the people, that's why the people are now reacting. We are the guardians of Orthodoxy,'' theology professor Nikolaos Vassiliadis told the cheering crowd.
Many of the speakers referred to the pontiff as the ``arch-heretic,'' a reference to the Great Schism which split Christianity into Orthodox and Roman Catholic branches in 1054.
``Because of this decision by our Orthodox Church, a pope will set foot on our holy soil for the fist time in more than 1,000 years,'' said Father Maximos.
With the exception of some clerics, most of the people at the gathering belonged to ultra-Orthodox fringe groups and followers of the ancient Julian calendar.
Many such fringe groups and Orthodox zealots have threatened to hold mass demonstrations during the papal visit.
Many at the gathering handed out leaflets calling on people to attend a number of protests being organized before the papal trip, including an April 25 rally outside Christodoulos' office at the archdiocese.
The scheduled stop in Athens is the first leg of a five-day pilgrimage following the footsteps of the Apostle Paul. The pontiff will then travel to Syria and Malta.
Greece will not be the pope's first visit to an Eastern Orthodox nation. But it is likely to be the most contentious - and possibly unleash some of the loudest protests in the pope's 23 years of world travels.
``Blood may be spilled because of this visit,'' said the Most Rev. Nektarios Moulatsiotis, who represents a strongly conservative faction within the Orthodox church.
``There will be great fanaticism ... People will take to the streets,'' said Moulatsiotis, who is best known here as the manager of a popular rock group of Orthodox monks.
The outrage toward the pope - and by extension the entire Roman Catholic Church - springs from deep within the Greek psyche.
Greek clerics see themselves as the caretakers of the ``true'' Christianity: the various Eastern Orthodox churches that encompass more than 200 million followers worldwide. The Orthodox split with the Vatican more than 1,000 years ago in a dispute over papal authority. The pope is regarded by some Orthodox as the leader of a wayward - or even heretical - flock.
``The two-horned, grotesque monster of Rome'' is how the pope was described by Greece's clerical union, which representing parish priests.
And there is even more baggage weighing down Greek perceptions of Roman Catholics.
The Crusaders are blamed for one of most painful moments in Greek history: the sacking in 1204 of Constantinople, the seat of the Orthodox Byzantine empire. The city, now Istanbul, fell to the Muslim Ottoman Empire two centuries later.
Caught in the middle of the growing storm is the leader of the Greek Orthodox Church, Archbishop Christodoulos.
Christodoulos, in fact, helped give the Orthodox fringe unity and credibility last year. He led huge rallies in opposition to the government's plans to strip religious affiliation from identity cards.
Now, the mix of faith and ultra-patriotism he brewed threatens to spill over during the papal visit.
``We are trying to control things. We are telling them to stay calm,'' Christodoulos said. ``This has wider ecclesiastical dimensions. Can you imagine the image of people holding up and waving crosses?''
He said the church's governing body agonized for nearly a year before taking its decision to welcome a pilgrimage by John Paul II.
``We had torturous meetings to decide,'' Christodoulos said. ``We decided we could not say no. A bad image of the church - that we are fundamentalists, non-Europeans - would take root.''
Among the 16 Orthodox churches, the Greek branch had been one of the Vatican's foremost critics.
``Fringe ecclesiastical organizations, with the silent support of a segment of the clergy, are already on a war footing, deeming the papal visit a religious sacrilege,'' columnist Petros Papaconstantinou wrote in the daily Kathimerini. ``Regrettably, Archbishop Christodoulos himself has provided ideological grounds for this religious fanaticism.''
``He's on a tightrope,'' said Metropolitan Chrisostomos of Zakinthos, who supports the papal visit.
Christodoulos has tried to appease critics by saying he will discuss concerns about the Eastern Rite churches with the pope. This could become a central issue during the pope's planned June visit to Ukraine, a predominantly Orthodox country where the Eastern Rite church is well established.