Lt. Col. Jeffrey Peterson, who goes outside the wire at least once a day to feel the pulse of his area of operations, was leading the mission. We would drive to the bottom of Haifa Street, walk up its length to assess the Iraqi Army's security preparations for the Shiite pilgrimage to commemorate the martyrdom of the Seventh Imam, which was about to start, and then mount up again for the ride to COP Remagen, where we would spend the night with the soldiers living there. Peterson gave a mission brief, instructed a soldier to tell a joke, and gave the order to armor up.

The colonel, two interpreters ("terps"), about 15 soldiers, and I piled into three Strykers; in each vehicle, one soldier drove, one manned a huge 50-caliber machine gun in the turret, one stood in the vehicle commander's hatch, two more manned 7.62mm machine guns in the rear hatches (I had the right rear hatch, but with no machine gun), and whoever was left sat inside the hull. Everyone with a crew position, including myself, was hooked into the vehicle intercom, and, as in the Humvees down at Kalsu, you have to wear a helmet at all times when inside a Stryker. Once everyone was in and we'd done a communications check, the ramp slammed closed and the three-Stryker column rolled out.

As we passed through the gate of the base, every soldier locked and loaded his weapon, whether an M4 carbine or a vehicle-mounted machine gun. A few minutes later, after passing through the International Zone's usual Peruvian and American checkpoints, we rolled into the narrow, grimy streets of Iraq's capital. "Harry Potter," Peterson said over the intercom as we passed through the last checkpoint, "you are now doing what 99 percent of Americans will never do."

From my hatch at the rear of the Stryker, I could see, for the first time, the people of Baghdad at close range: clusters of bored-looking young men, gaggles of grinning children, small groups of women in full, flowing black burqas. The drive to the bottom of Haifa Street, at the southern end of 1-14's area, was a short one, and before long we came to a halt and the order to dismount came over the intercom. The ramp slammed down, the soldiers rushed out and took up positions on both sides of the street, their carbines pointed outward, and after pausing for a split second to think how utterly unfamiliar a situation I was in, I jumped down after them. I was in Baghdad - real Baghdad.

While my mind raced to orient itself to a vaguely remembered map of Haifa Street, the squad of riflemen fanned out from the three Strykers into a patrolling formation, with Lt. Col. Peterson toward the front-center. As the ramps went up and the formation began to move forward, slowly, I took up a position to the colonel's rear, next to his terp, a Baghdad native who went by the pseudonym "Mark." For a minute or two it was sensory overload: the dusty main road, pools of thick brown water by the sidewalks, an overwhelming smell of sewage, rickety awnings hanging over the doors to innumerable grimy shops, and of course the heat - not too bad, 115 degrees maybe, but with a slight and unwelcome breeze, which made it feel like I was standing inside of a hair dryer.

The first coherent thought to run through my head was that I was in a neighborhood not too different from an old Muslim quarter I wandered into in Delhi in 2006: mud-brick houses, dust, stands selling meat either raw or grilled, and twisting, ancient-looking alleys branching off the main road after every block. The main difference, it occurred to me after a moment (besides the heat and the presence of a squad of formidably armed and armored US soldiers) was that the people seemed more welcoming: as Peterson walked down the sidewalk, greeting shop owners and residents with a well pronounced Salaam aleikum, I was struck by the people's demeanor.

Scrawny, white-haired, jagged-toothed men smiled up at the colonel from their seats, responding with a pleased-sounding Aleikum as-salaam, and middle-aged men did the same. The women, mostly wearing black robes that covered everything but their face, either greeted us as we walked by or simply smiled back at our greetings. Among younger men there was more of a split: some were enthusiastic, recognizing the colonel or his soldiers and greeting them in English, while others kept their expressions stonily cold, offering us no recognition whatsoever. Children of every age, both boys and girls, clustered around each of us, calling out "Hello mister!" or "Chocolata mister!" and grinning hopefully; many stuck out their hands for high-fives, fist-pounds, or handshakes.

When they clustered too close around me, Mark shooed them away with a firm Imshi, habibi, and they moved on to the next soldier in the formation. Two ragged-looking Iraqi soldiers - "jundis" - manned a minimalist checkpoint (a string of concertina wire and nothing else). Peterson approached them and asked, through Mark, whether they were going to keep the area safe for the pilgrimage tomorrow; they eagerly assured him that yes, they would do their best. Their slouched posture and mismatched uniforms didn't lend them credibility, but their confidence was a little reassuring, as was the cleanliness of their AKs. Another encouraging sign, and a surprising one, that the colonel remarked on and asked the jundis about was the scarcity of posters of Muqtada al-Sadr - Badr-type posters of ageing, moderate Shiite clerics were everywhere, but we saw Sadr's puffy form only here and there. Even more strikingly, there was very little trash.

It was clear that this was one of the streets that 1-14, and the colonel himself, patrolled regularly. "You have to dismount, get out there on the ground, and talk to people," the colonel had told me earlier in the day - "There is no other way." On these few blocks, it could not have been more obvious that the squadron's soldiers were following this guidance, straight of classical counterinsurgency doctrine, and to good effect.

The cheery, welcoming attitude and bustling shops we saw near our dismount spot did not last long, though. A few hundred yards from where we'd dismounted the Strykers, we reached a wide intersection: we were turning onto Haifa Street proper. The COP, our destination for the night, was to the north, but maybe 500 yards to the south we could see unusually large clusters of people, many of them in black robes and some carrying green or black banners emblazoned with golden Arabic calligraphy: the lead edge of the northward-bound stream of pilgrim.

Faintly, from farther down the road, the boom of drums was audible, mixed with singsong Arabic chanting; it grew closer by the second. Without hesitation, the colonel gave the order for the patrol to turn south and get as close a look at the crowd as possible before taking up a position to watch the night's marchers pass by at close range. While the Strykers rolled around the corner and took up an overwatch position at the intersection, ready to deliver fire or extract us in case of emergency, Peterson led the patrol south, along the east side of the street, at a more deliberate pace. The chanting was growing louder and closer as we moved toward the pilgrims, and the soldiers, who had seemed relaxed before, now appeared vigilant, holding their carbines at the ready and steadily scanning their sectors for anything untoward.

To me, though, everything seemed untoward as we came to a halt in a set of doorways near the fringes of the crowd: Iraqi soldiers and police were watching like hawks from the sidewalks and from an armored vehicle, their AKs unslung and ready for use, and with every second more and more black-clad pilgrims moved into view from the south, chanting and bearing ornate banners. Where a minute before there had been a large crowd of people, there was, very suddenly, an absolutely massive horde, literally thousands of pilgrims slowly pushing forward.

The crowd was as dense as the insides of Fenway Park, and much louder: the chanting was becoming deeper, louder, and, to my ears, more menacing. The soldiers looked as wary as I felt, but not the colonel; as we came to a stop, he welcomed an Iraqi CBS cameraman and agreed to do a quick interview, to the security squad's apparent irritation. While Peterson and Mark talked with the cameraman, confirming with a cell phone call to his boss, Baghdad correspondent Laura Logan that he was who he said he was, the soldiers watched the black mass of Shiite pilgrims carefully.

For a while, the main Iraqi commander in the area, Brig. Gen. Baha (commander of the 5th Brigade, 2nd Iraqi National Police Division) stopped by with his security detail as well. As darkness began to set in, some of the soldiers donned night-vision goggles, but there were streetlights, too, allowing me to watch the northward advance of the crowd. As the pilgrims poured north, the nature of the crowd changed: where before it had been unorganized, the women and children were now at the edges, nearer to the sidewalks, singing and chanting, while the men marched in the center, lashing themselves with chain flails to the beat of the drums. At the very core of the crowd, a cluster of men marched by, surrounded by hundreds of others with their chains, bearing a green-draped coffin - the symbolic coffin of the Seventh Imam, whose death the crowd was mourning by flagellation.

There was something surreal and almost medieval about the scene: a coffin carried on chanting men's shoulders, a huge case with a gleaming white light right after that, thousands of men chanting to the sound of drums and thrashing themselves with bloody chains, young boys emulating them by hitting their backs with their hands, and the women and girls singing and swarming at the edges the whole while. I would learn the next day that this was only the beginning of the march and that the crowd I was seeing now was nothing to what would come later, but it was an unbelievable sight.

After maybe half an hour, when darkness had fallen completely, only the tail end of the crowd was left, with the chanting and drums fading off to the north. Besides a few stragglers, Haifa Street was deserted, and it was another 15 minutes or so, as we began to move north as well, before local residents began to trickle out of their homes to resume their evening activity in the wake of the marchers.

In the Holland Apartments, a cluster of high-rises built years ago by a Dutch company, maybe a fifth of the windows had lights on inside, apparently an impressive amount since many of the residents who had fled before the January battle had yet to return. Huge tents that had been providing tea and water to the marchers now stood nearly empty, allowing us to go inside and talk with the men who had been handing out the refreshments - men who unabashedly wore badges marking them as officials of the Office of the Martyr Sadr, one of the various political wings with connections, present or historical, to the Mahdi Army and Muqtada al-Sadr.

As the squad came to a halt so that Peterson could play foosball (they called it fishi) with some local children and talk to their fathers, the three Strykers rolled by, heading up toward the COP to park for the night; we would walk the rest of the way. With the crowd gone, the soldiers and both terps were visibly more at ease, even as we passed another Iraqi checkpoint (a bit of concertina wire and some blankets to sleep on when off duty - a force protection nightmare) into the Sunni neighborhood of Saddamiya, just south of the COP, where al Qaeda's main stronghold had been during the January fighting.

As we pushed through Saddamiya, I couldn't see my own feet, it was so dark, but the soldiers had their night-vision devices, and my brain stopped for a moment again to tell me how truly bizarre my surroundings were: walking forward in complete darkness, the only light the faint green glow of one nearby soldier's night goggles, through a ruinous, blacked out neighborhood that at the time of Princeton intersession had been the scene of a deadly battle between Stryker soldiers and heavily armed concentrations of al Qaeda and Tawhid wal-Jihan terrorists. As we walked down the last block of Haifa Street toward the trees at gate of the COP, Lt. Col. Peterson walked by me and said, from the blackness: "Now you can tell people you walked the length of what six months ago was the most dangerous street in Iraq."

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