Just as in 1861, officers shouted commands over the din of battle, the air shook with the concussion of artillery and ranks of grimy, perspiring men leveled weapons at each other under a blazing July sun.

They fought the Battle of Bull Run again Saturday - an estimated 8,700 Civil War reenactors, observed by 11,000 spectators who packed into bleachers and lined the "battlefield" despite the searing heat and high humidity.

The reenactment, held on adjacent farm fields in Gainesville, was staged to mark the 150th anniversary of the July 21, 1861, battle, which was the first major clash of the war and in the South is often called the Battle of Manassas.

It was a humiliating defeat for the Union army and a triumph for the Confederacy.

The reenactment was the latest in a series of commemorations of the battle and the most recent event to mark the ongoing sesquicentennial of the Civil War years.

Saturday's fight saw no major battle injuries, but some reenactors — many of whom wore heavy wool period uniforms — and spectators were treated for heat exhaustion.

Joseph Robertson, a battalion chief with the Prince William County Department of Fire and Rescue, said 148 people were evaluated at the site of the reenactment in two air-conditioned medical tents and 11 people were taken to local hospitals.

Ann Marie Maher, executive director of Discover Prince William & Manassas, which organized the event, said people were treated for such ailments as heat exhaustion, insect stings and sprained ankles.

A few reenactors sought to beat the heat by placing ice cubes on their heads beneath their caps. Others were cooled by a benevolent female reenactor who went through the ranks spraying soldiers' faces with water from a spray bottle.

Spectators flocked to cooling tents equipped with huge fans, or chugged ice water, cold sodas and bottled water.

The day began with a hazy, orange sun rising over the large 1860s-style encampment, where reenactors from across the country had set up hundreds of white tents and spectators were arriving before 7 a.m.

The surrounding woods filled with campfire smoke and the sound of neighing cavalry horses as the soldiers rose and prepared for battle.

The reenactors, men and women, came from many walks of life. There was a banker, a retired librarian, a nurse, a retired police detective and numerous teachers. Most looked hot beneath their Civil War-era clothes but seemed to be having fun.

"It's nifty," said John Stengel, 64, of Cuba, N.Y., who stood perspiring in the dark-blue wool tunic of a private in the 6th New Hampshire regiment.

"It's physically very uncomfortable," he said. "But, man, when this column swings out into the road and that band is playing and everything, you can be back in 1861. You really can.

"You look around, you don't see anything modern," he said. "Dust is coming up from the road. And this is authentic Civil War weather. Of course, there's a few things they experienced that we didn't, like we're not worried about getting our heads blown off or anything like that."

Stengel, like other reenactors, had cotton stuffed in his ears. "The gunfire will make my ears ring," he said. "I can hardly imagine how any of [the Civil War soldiers] got through an engagement and still had any hearing."

As the time for the reenactment neared, "Yankees" and "Confederates" assembled to march to the battlefield.

A line of rebels, clad in straw hats and blue-and-white-striped pants, said they were with the First Louisiana Special Battalion, known as Wheat's Tigers, for their commander Roberdeau Wheat.

A unit marching along the road in red shirts called out that they were with the 2nd Mississippi regiment. Another Confederate outfit, wearing green shirts, said they were the "Gist Rifles" and part of the Hampton Legion.

The Battle of Bull Run was notable for the array of uniforms worn by men on both sides, before the standard blue and gray garb that came later in the war.

At one point, Scott Sharp, 41, a high school teacher from Stoutsville, Ohio, stood in a red shirt with a black tie and black hat giving a pep talk to the men portraying the 13th New York regiment, who were lined up before him.

The 13th "was one of the first units on the field," he told the men, a sword hanging by his side. "Took a ton of casualties, mainly because they didn't run away. They fought hard. They were one of the last units off the field, covering the retreat of the federal army. We will not run. Just so you know what we're about today."

Elsewhere, women in hoop skirts holding baskets of green apples, bread and cell phones waved handkerchiefs embroidered with their husbands' names as the rebel infantry marched toward the battlefield.

Wearing a red-checkered cotton hoop skirt and wide-brimmed straw hat, Amber Hancock, 29, of Section, Ala., scanned the sweaty faces for her husband, Terry, a Confederate colonel.

She dabbed her face with a white handkerchief and confessed she wasn't wearing her pantaloons because of the heat.

The two met at a reenactment of a Civil War skirmish and dance in Alabama.

"I asked him to dance and he said no," Hancock said. "But he contacted me the following week to apologize and said he was just shy." The two dated for two months and were married five years ago.

As their men marched away to the cadence of a fife and drum, the women called after them.

"God bless y'all," they said.

"Y'all come back safe."

The reenactment is scheduled to be repeated Sunday.