Joe MacPhail was one of hundreds of casualties in yesterday's reenactment of the First Battle of Manassas, but it wasn't a Yankee bullet that felled the Chesapeake, Va., man.

MacPhail, who portrayed a Rebel soldier in the Civil War skirmish, collapsed from heat exhaustion and spent 20 minutes recuperating in an emergency tent staffed by Fairfax County fire and rescue workers, who supplied cold drinks and medical attention to nearly 300 victims of the mid-90s heat. It was one of the few concessions to modern life in the otherwise authentic reenactment, and MacPhail was grateful.

"A hundred and twenty-five years ago, they didn't have a rescue squad," he said, slinging his five-pound wool uniform jacket over his arm. "You just lay down and crossed your fingers."

More than 50,000 spectators came to a dusty 500-acre plot of land in Centreville for the reenactment by more than 5,000 weekend warriors, according to the American Civil War Commemorative Committee, which organized the event to honor the 125th anniversary of the beginning of the war that divided a nation.

Half a million rounds of small arms fire were expended, and 1,500 rounds were fired from 50 cannons. It was the largest reproduction of a Civil War battle ever, the committee said.

Ten people were taken to nearby hospitals for treatment, including one man who may have broken a hip when a horse fell on him, said Lt. Leonard Murry of the Fairfax County fire and rescue service.

There were traffic maladies, too: Cars overflowed the 12,000-space parking lot and backed up on Rte. 66 more than a mile from the site.

The first battle at Manassas -- or Bull Run, as it is known north of the Mason-Dixon Line -- actually occurred five miles from yesterday's fighting field, on July 21, 1861.

The Union Army, which had expected such an easy victory over the Confederate rebels that family members and friends brought picnics to the battle site, was forced into an embarrassing retreat. Nine hundred men died in 10 hours of fighting. The North learned then that the war would be a long one.

The Union troops fired the first shot, aiming a diversionary attack directly at the Southern troops while the bulk of the Union troops headed for the Confederates' left flank. The outnumbered rebels fled.

The Union army paused to regroup, and Southern reinforcements arrived. The fresh rebel troops fought fiercely, slamming into the Union's right flank. The federals were pushed into a panicked retreat.

Yesterday, 10 hours of battle were compressed into 2 1/2, and the mood was lighthearted. Young children pressed against snow fences surrounding the battle site and shouted as cavalry units pounded across the plain. Families picnicked behind the lines, adults trading bottles of beer and tales of other reenactments they had attended. Rifles cracked, and puffs of white smoke clouded the battlefield.

Lorna Lewis, 29, of Cottonwood, Ala. ("We drove 900 miles to get here") cheered as her husband's unit, the red-hatted Louisiana Tigers, charged into view. She said she and her husband, a high school mathematics teacher, go to several reenactments a year. It is an expensive hobby, she said: A uniform costs about $60, boots $70 and a weapon $435 or more.

Lewis, her husband and two children had spent the previous few days at the encampment, which resembled those of Civil War days; many other participants did likewise. They dined Saturday on Louisiana-style jambalaya cooked in a huge iron pot. Like other Civil War buffs at the gigantic gathering, she said she enjoys the history education and good fellowship of battle reenactments.

"You get addicted," she said. The fact that the South won this battle pleased her: "We always like it when our guys win. But they seem to enjoy it both ways."

Nearby, Rebecca Ramsay of Nashville tried to stir up a breeze with a wooden fan as she sat on a quilt in her long red-and-white cotton gown, hand-crocheted gloves and a feather hat. She delicately moved the folds of her skirt to reveal a hidden bottle of Sprite, a luxury not permitted the soldiers, who were allowed only water from canteens.

Her 15-year-old son, whose great-great-grandfather fought with the Confederacy, was playing a rebel soldier on the steamy field of battle, in authentic dress "down to the long underwear."

"I was so thrilled in this time of drugs and rock 'n' roll that he should have this interest," Ramsay said.

"It's a hobby," said Linda Shaw, 37, of Bridgeton, N.J. "Instead of playing golf, they put their time into this." Shaw's husband, whose ancestors fought on the Union side, wore red pants, a blue jacket and a silk bow tie in his role as a New York soldier.

Lounging under a stand of hardwood trees a short walk away were Mike Grossi, 47, of Houston and George Hoad, 31, of Ontario, both portraying Rebel soldiers dropped by Yankee bullets -- even though, they joked, Union soldiers could barely shoot straight.

Grossi shares a birthday -- Jan. 21 -- with Stonewall Jackson, who acquired his nickname at Manassas. That prompted Grossi to write a paper on Jackson in junior high. "I've been fascinated every since," he said, adding that he attends as many as 10 reenactments a year.

Hoad, wiping his forehead with a blue bandanna, said he goes to reenactments because of a "love affair with a valiant struggle, a lost cause -- and escapism. Hell, the atomic bomb is 80 years away."

The Confederacy "was doomed from the beginning, yet they fought on valiantly," he said. "After this, it was no longer a gentleman's war."