Karbala, 60 miles southwest of Baghdad, is usually no more than a 90-minute drive through an increasingly green landscape of date palms, eucalyptus trees and reeds watered by the nearby Euphrates. But for most of a week this past October, the journey turned into a five-hour crawl. Highways leading to Karbala were choked by an enormous mass of humanity heading toward the city to celebrate the birth of the 12th Imam, a redeemer born more than a thousand years ago who disappeared as a child and, so these travelers believe, will one day return to overthrow all tyrants. Many walked all the way from Baghdad—crowds had been streaming out of the city since midweek—while others had set out days earlier from towns as far away as Nasiriyah, in the deep south, and Kirkuk, 200 miles north of Baghdad.

Despite dust and 90-degree heat, the pilgrims, many of them barefoot, kept up an urgent pace. The flags they carried— mostly bright green, but also red, yellow, pink—made brilliant splashes of color in the flat landscape, contrasting with the all-enveloping black abayas of the women. They marched in separate groups, parties of friends or neighbors, until they drew close to their destination and coalesced into one dense column. Every so often a group would break into a rhythmic chant, invoking the names of the martyr-saints that inspire their faith. “We are Shia,” the men roared in unison, stabbing their fists in the air. “We are the sons of Imam Hussein, and the name of Ali is always on our tongues.” Shiites or Shia—the terms are used interchangeably and both mean “partisans”—form one of the two great branches of Islam. About 150 million Shiites are spread around the world, most of them in Iran, Iraq, India and Pakistan. While the Sunni branch makes up the greater part of the global Muslim population of more than a billion, Shiites form the majority in Iraq—as many as 15 million out of a population of 24 million. Nonetheless, Shiites have never held power in Iraq nor fully participated in its government, and at times have been brutally repressed.

The future role of the Shiites is one of the most important issues facing Iraq. Now that their greatest oppressor, Saddam Hussein, is gone, they will no longer tolerate second-class status. At the same time, others in Iraq and elsewhere, including many in the United States, fear that a Shiite-dominated government might impose an Iranian-style fundamentalist Islamic regime. If a democratic Iraq is to emerge from the ruins bequeathed by Saddam Hussein, both the hopes of the Shiites and the fears of non-Shiites will somehow have to be accommodated.

Iraqi Shiites are a diverse group. Some are educated and middle class, but most are poor Arabs living in rural southern Iraq or Baghdad’s slums (there are significant communities among the non-Arab Kurdish and Turkmen peoples of the north as well). They range from the deeply religious to the wholly secular. Their common bond is a memory of discrimination, whether in the form of the mass executions common during the reign of Saddam Hussein or simply in their exclusion from power throughout Iraq’s history.

Today, the Shiites are confident that those days ended with the fall of Saddam Hussein. “Everything is changing,” Adil Abdul Mehdi, a leader of a powerful Shiite party, told me cheerfully in Baghdad, as we sped across town in a convoy of SUVs, surrounded by armed bodyguards. “For too long the Shia have been a majority that acted like a minority. They have to raise their heads. They have a right to represent Iraq.”

Now, on the road to Karbala, I was watching the Shiites assert one of those rights: the freedom to celebrate one of their great religious festivals. Fifteenth Shaban, as the festival is called, is the date in the Muslim calendar (October 11 this year) that marks the birthday of the 12th Imam. By the evening of the festival, well over a million people were crowded onto the vast plaza surrounding the two colossal shrines crowned with golden domes and minarets that dominate the center of the city.

Karbala is a holy place for Shiites because of the two men buried in those shrines. Half brothers, they died in a battle here long ago, a battle that grew out of a ferocious struggle to lead Islam after the death of the prophet Muhammad in a.d. 632. The Shiite faith originated with those Muslims who thought that the wrong side—that led by Abu Bakr, fatherin- law of the prophet Muhammad—won, unjustly usurping Muhammad’s cousin and son-in-law, Ali. (Sunnis believe that Abu Bakr was the rightful heir.) Ali did finally become caliph in 656 but was assassinated five years later and buried in nearby Najaf. Shiites regard Ali’s brief reign as the last period of legitimate and just rule on earth.

Nineteen years after Ali’s death, his second son, Hussein, who had been living without evident political ambition in Medina, responded to a call from the people of Kufa, then chafing under the harsh rule of a Sunni caliph, Yazid, and set out across the desert to lead them in rebellion. It is a fundamental tenet of Shiism that Hussein’s motivation was not power lust but revulsion at Yazid’s tyrannical rule. As one cleric in a theological school in Najaf assured me, “When Imam Hussein left Medina, he said, ‘I’m not going to win a fortune or a throne. I am going out for justice,’ even though he knew he was going to be sacrificed.” Indeed, many believe that Hussein knew before he left Medina that his supporters had been rounded up and that his cause was doomed. Intercepted by the caliph’s army on the plain of Karbala after a long journey across the desert, Hussein and his band of 72 family members and followers refused to surrender, digging a ditch behind them to preclude retreat. The saga cherished by Iraqi Shiites recounts how, in the midst of battle, Hussein’s warrior half brother Abbas heard the women and children crying from thirst. Fighting his way to a nearby stream to fetch water, he was cut down. Hussein, fighting on a few hundred yards away, was the last to die, sword in one hand, Koran in the other.

This religious schism between Sunnis and Shiites is not, however, mutually antagonistic in the manner of Catholics and Protestants in Northern Ireland or Christians and Muslims in Beirut. “My mother is Sunni, my father Shia,” says Baghdad native Fareer Yassin. “One third of the Muslims in my high- school graduating class were from mixed Sunni Shia marriages, and that was typical of Baghdad.” I have heard similar stories from many Iraqis, who also point out that direct clashes between the two communities are extremely rare and that discrimination against the Shiites has inevitably been orchestrated by rulers—whether kings or Saddam Hussein— for political, not religious reasons.

For the masses of faithful pouring into Karbala for the festival this past October, the ancient battle at this site might well have happened yesterday. Strolling late in the warm evening through the vast crowd around the shrines of Hussein and Abbas, I heard constant reaffirmations of support for the long dead heroes. “See the love that people have for Imam Hussein,” said my guide, Ala’a Baqir, a pharmacist influential in local affairs. “He is for justice, and people think we are losing that in our own time. We are ready to fight at any time for Imam Hussein.”

It would be easy to dismiss such assertions as simply the celebration of a folk myth, but the saga of the martyrs has preserved a potent philosophy at the core of the Shiite faith. “Shiites regard the opposing of injustice and tyranny and fighting against an unjust ruler as a supreme religious duty,” explained Hussain Shahristani, a nuclear scientist, devout Shiite and lifelong rebel, as we sat in the Karbala office of the humanitarian relief group he founded and directs. He cited the great national uprising of 1920 (his father’s first cousin was one of its leaders) against the British, who occupied Iraq between 1917 and 1932—and effectively controlled it until 1958. Although both Shiites and Sunnis joined the revolt, Shiite religious and tribal leaders played the major role. Politically, the failed rebellion proved disastrous for the Shiites, since the British thereafter relied exclusively on the Sunni elite to govern Iraq. But, says Shahristani, Shiites “couldn’t do anything else. It might be politically better to just go along with the master, but for us that’s impossible.”

Shahristani speaks with authority on the topic of dissent. In September 1979 he told Saddam Hussein to his face that building a nuclear weapon was wrong and refused to work on the project. He was tortured and spent 11 years behind bars, 10 in solitary confinement. During the Gulf War in 1991, he made a daring escape—he stole a guard’s uniform and drove out the prison’s main gate. Afterward, he declined a comfortable exile in the West in favor of organizing humanitarian aid for both Iraqi refugees in Iran and anti-Saddam resistance in Iraq.

I found Shahristani’s views echoed by religious authorities, who made it clear that this obligation to resist applies even to the American-led occupation, of which the Shiites are increasingly resentful. In a modest house in the center of Karbala, Sheik Abdul Mehdi Salami, who leads the Friday prayers at the Hussein shrine (an immensely prestigious position), said that “fighting injustice is the principal duty for all Shia.” “For the meantime,” he added, his people were using “peaceful means” to assert their rights from the coalition and that Shiites do not like “killing and blood.” But if they must, they will “sacrifice everything to get their rights.”

Compared with what they endured in Saddam Hussein’s time, the Shiites today appear to have little cause for complaint. Saddam not only had banned all public religious processions but, according to worshipers I spoke to, particularly disliked the notion of a 12th Imam who would return to overthrow tyrants. As a result, anyone who attended the birthday festival during Saddam’s rule was risking his life. Strolling with me through the crowd on the eve of the festival, Ala’a Baqir recalled how celebrants would evade Saddam’s security forces on the main roads by sneaking through fields and palm groves. “We would go out and leave food and put down little lights to guide them,” said Baqir.

This year, for the first time in decades, there was no need for surreptitious measures, and the plaza was alive with light and the noise of declaiming preachers and chanting marchers—“we are the Shia . . .”—against the background noise of several hundred thousand people. Above us, party balloons soared up past the golden dome of the Abbas shrine.

Yet even this happy atmosphere harbored ominous undercurrents. A coffin was carried around the Hussein shrine—a traditional Shiite rite—but this one contained the body of a man killed the night before in a firefight with American soldiers in Sadr City, the vast Shiite slum in northeast Baghdad. I began noticing how many young men in the crowd were wearing white burial shrouds over their shoulders, a symbol of their willingness to die as martyrs, an attitude much favored by supporters of Muqtada al-Sadr, the 30- year-old extremist whose men had ambushed and killed two American soldiers in that firefight.

For centuries, Karbala and its sister shrine city, Najaf, had been islands of Shiism, well connected to the international Shiite community but with few ties to the nomadic Bedouin tribes roaming the desert just beyond the cities’ gates. Only at the beginning of the 19th century did the clergy of Karbala and Najaf begin to convert the desert tribes, partly because they needed muscle to defend against increasing attacks by fanatical Wahhabi Sunni sweeping across the desert from what is now Saudi Arabia.

At the same time, Shiite clerical leaders decided that only the most learned among them should be allowed to issue fatwas, religious rulings on matters of law or common concern. These few senior figures became known as “sources of emulation.” One hot day in late September I sat in on a class at Najaf’s 900-year-old religious university conducted by one of four such living sources of emulation, the Pakistan-born Ayatollah Bashir al-Najri. My classmates were turbaned, graywhiskered elders. We sat respectfully on the floor while our revered teacher expounded at some length on the requirements of women to perform ritual ablutions. Some parts of the syllabus, I felt, had probably not changed over the centuries.

The Shiite religious leadership gained power and influence in the last years of Ottoman rule, just before World War I, then fell on harder times during the British occupation and the succeeding Sunni monarchy installed in 1921. “The first Shia prime minister was appointed in 1947,” Adil Mehdi said bitterly. “That was nearly 28 years after the founding of the state. Though the Shia represented 60 percent of the population, we only ever had 20 percent of the cabinet posts.”

In hopes of bettering their lot in the 1950s and early ’60s, many Shiites were drawn to radical organizations, principally the Communist Party but also the Arab nationalist Baath Party. Thus, when the monarchy was swept away by a leftist revolution in 1958, the Shiites were at last represented in the radical military government that assumed power. But that regime was overthrown in another coup five years later, and the Shiites’ brief moment in the sun came to an end.

Though the Baath Party had originally numbered many Shiites among its leaders, by the time it began its 35-year rule with a coup in 1968, the leadership was solidly in the hands of a tight group of Sunni tribesmen, including a ruthless hit man named Saddam Hussein, from the region around Tikrit. Apart from hunting down and killing their former Communist rivals, Saddam and his militantly secular colleagues also took aim at the Shiite religious leadership.

In response to the wholesale defection of many of their flock to the Communists, the Shiite religious leadership made efforts to modernize their message and attract new followers. Prominent among them was a brilliant scholar named Muhammad Baqir al-Sadr, the principal sponsor of Dawa, a radical Islamic political party that confronted the Baathists as an opposition group throughout the 1970s.

The confrontation intensified after Ayatollah Khomeini, himself a Shiite who had spent most of the 1960s and ’70s in Najaf developing his theory that clergy had the exclusive right to govern, seized power in Iran in 1979. Sadr, thrilled by Iran’s mass Islamic uprising against the shah, thought a similar religious takeover of the government was possible in Iraq. Saddam, apparently worried that Sadr might be right, launched a campaign to round up his supporters. In April 1980, Sadr and his sister were arrested and executed.

Shahristani, the nuclear scientist and prison escapee, was close to Sadr. He told me that at the end, the Baathists offered Sadr a deal. “They said they would release him in exchange for a promise of silence. Sadr said, ‘No. I have closed all the doors, there is no escape for you. Now you have to kill me so the people can rise up.’ ” As any Shiite would immediately understand, it was an embrace of martyrdom that echoed the self-sacrifice of Hussein 1,300 years before.

Both Sadr’s hopes and Saddam’s fears proved groundless. The people did not rise up, and in the eight-year war that followed Saddam’s invasion of Iran in September 1980, Shiite conscripts for the most part fought doggedly for Iraq, largely motivated, despite their grievances and persecution, by Iraqi patriotism.

But after the 1991 Gulf War, inspired by calls for an uprising from Washington, Shiites finally erupted in furious rebellion. That the expected U.S. assistance never came has hardly been forgotten.

Nobody knows how many people were killed in Saddam’s savage reprisals for the uprising, but the number is at least in the tens of thousands. One mass grave of those slaughtered has alone yielded more than 3,000 bodies, and hundreds of such graves have been unearthed. Ironically, the Baathist’s savagery helped unify the diverse Shiite community. In the 1990s, even while cracking down viciously on Shiite religious leadership, Saddam made attempts to bolster his support among religious conservatives by encouraging such Islamic practices as the veiling of women, the segregation of the sexes in schools and the prohibition of alcohol. (Gestures to appease Shiites included repairs to shrines and a manufactured family tree tracing Saddam’s ancestry back to Ali.) But while the measures helped revive traditions, they produced no corresponding support for the dictator.

Toward the end of the decade, Shiites found a leader in the person of Muhammad Sadiq al-Sadr, a teacher from Najaf and a distant relative of the resistance leader executed in 1980. Initially encouraged by the regime because of his denunciations of the United States, Sadr II, as he is often called, set up a network of followers across southern Iraq and in Baghdad. Late in 1998, though, he began wearing the white martyr’s shroud while denouncing Saddam’s regime to growing and enthusiastic crowds. In February 1999, while driving home in Najaf, Sadr, along with two of his sons, was duly machine-gunned to death by state security agents.

Today, portraits of Sadr II, who is invariably depicted as a humble ancient with a snow-white beard, adorn walls and billboards around Iraq. These frequently share space with bearded, turbaned portraits of other Shiite leaders, many of them dead—testimony to the high mortality rate in Shiite religious politics. A few hundred yards from the site of the al-Sadr murder, for example, is a green-domed tomb, still under construction, that contains what few remains could be collected of the late Ayatollah Muhammad Baqir al- Hakim, founder and leader of a political party called the Supreme Council for the Islamic Revolution in Iraq. He was the victim of a massive car bomb that exploded as he was leaving Najaf ’s Imam Ali shrine on August 29 this year.

Hakim was almost certainly killed by former members of Saddam’s security services now active in the resistance and determined to eliminate anyone, like Hakim, who cooperated with the Americans. However, at the funeral ceremonies, attended by hundreds of thousands of Hakim’s followers, Abdel-Aziz al-Hakim, his brother and successor as leader of the party, bitterly denounced the occupation forces for their failure to protect Hakim. It seemed that at least some Shiites were finding reasons to criticize their new rulers.

I viewed the massive destruction caused by the Hakim bomb during a trip to the shrine to see where a man I once knew had also been murdered. Last April, Abdul Majid al- Khoei, the son of a grand ayatollah, had just returned to Najaf—with the blessing of coalition forces, who appreciated his energy and liberal views—after 12 years of exile in London. Just inside the courtyard of the Ali shrine, a mob attacked him. Two companions were stabbed to death, but Khoei managed to escape and run the 50 or so yards that brought him to the front door of a house belonging to Muqtada al-Sadr, the radical Shiite extremist, who is a son of the martyred Sadr II. Khoei pleaded for shelter, but although there is little doubt that Muqtada was inside, the door did not open. Ashopkeeper finally took Khoei in, but the mob followed, dragged him down the street and round the corner, and knifed him to death.

Muqtada has always denied having had any role in the killing, though no one in Najaf that I talked to doubts his responsibility. Khoei not only believed in cooperation with the occupation but also stood for the separation of church and state, as opposed to the Iranian system of clerical rule, which Muqtada has endorsed.

On the day I retraced Khoei’s desperate flight, Muqtada’s well-guarded door was open and his front room crowded with petitioners seeking his help or advice. Three clerics sat at a table collecting wads of bank notes contributed by the faithful. Six months after the invasion that toppled his father’s killer, Muqtada was embroiled in an escalating conflict with the coalition forces and seemed to welcome any opportunity to confront them or, for that matter, other Shiite groups. Muqtada certainly enjoys a large amount of support among the poorer Shiites, most particularly among young unemployed men in the great Shiite slum of SadrCity in Baghdad. In the week following the peaceful 15th Shaban celebrations in Karbala, Muqtada’s gunmen attempted to take over the Hussein shrine in a shootout with supporters of a rival leader that left several dead and wounded on both sides. A few days later, they fought a U.S. patrol near the shrine, killing three Americans. (There were reports of a U.S. crackdown on Muqtada as we went to press.)

Opposing Muqtada in Karbala had been a shrine protection force loyal to perhaps the most important and revered Shiite leader in Iraq, Grand Ayatollah Ali Sistani. Sistani, 73, was born in Iran but moved to Najaf more than 50 years ago to study. He spent much of the 1990s under the baleful surveillance of Saddam’s security forces. Yet from his house, he maintained an extraordinary moral authority over the Shiite masses. When, in mid-April, there was an erroneous radio report that Sistani’s house was under siege by followers of Muqtada al-Sadr, the news spread like wildfire. “I was sleeping in a village near Basra that night,” recalls Hussain Shahristani. “Suddenly I saw the villagers grabbing their guns and preparing to rush to Najaf, hundreds of miles away. ‘Sistani is under attack,’ they told me. That was all they needed to know. The same thing happened all over Iraq.”

Though he has denounced violence and the proliferation of firearms in Iraq, Sistani himself has command of a far more potent weapon—the immense authority of his fatwas. Last July he addressed the fundamental question of how he wanted the constitution for Iraq to be written. The occupation authorities had endorsed a plan by which their handpicked governing council would appoint a committee that would in turn devise the new constitution. In a fatwa written in graceful classical Arabic, Sistani declared that this approach was “unacceptable” because there was no guarantee that a constitution produced in this way would “represent the (Iraqi) National identity of which Islam and the noble values of society are an integral part.” (Sistani has always rejected Khomeini’s thesis on direct clerical rule.) Instead, he insisted, anyone writing a constitution would have to be elected. A constitution devised by any other means, he made clear, would be “illegitimate.”

The story goes that when Paul Bremer, the head of the Coalition Provisional Authority, sent a message to the venerable religious leader suggesting that the two men cooperate on the constitution, Sistani sent a message back: “Mr. Bremer, you are an American and I am an Iranian. I suggest we leave it up to the Iraqis to devise their constitution.”

Few in Iraq believe that a constitution denounced by Sistani would stand a chance. But any fair election would almost certainly deliver a Shiite-dominated constitutional assembly. The underdogs and rebels would at last be in power—a sea change for a group that has so long defined itself through resistance to oppression. Will the Shiites still celebrate martyrdom when they are, themselves, in power? And who will judge them if they prove unjust?