’The Battle of Bull Run’ diorama, built by Don Ray and Paul Henderson, can be viewed at Miniature World in Victoria B.C. (George Devlin/GEORGE DEVLIN/MINIATURE WORLD)

William Howard Russell, the London Times war correspondent, went to the Battle of Bull Run in a rented buggy with a bottle of tea, a flask of Bordeaux and a container of brandy.

Sen. Henry Wilson, of Massachusetts, attended with a load of sandwiches to give out to the soldiers from his state.

Washington Judge Daniel McCook, from the family soon to be known as “the fighting McCooks,” grabbed his rifle, some politician friends and a picnic hamper and went out to join his soldier son, Charles, 18.

Despite the stifling summer weather — never mind the prospect of bloody combat — scores of onlookers, with parasols and opera glasses, in carriages and on horseback, flocked from Washington to the fields near Manassas for the first big battle of the Civil War.

They expected it to be the only big battle.

Instead, it became one of the most bizarre affairs of the long conflict — warfare as spectator sport, followed by a wild dash for safety — and it happened on July 21, 1861, 150 years ago Thursday.

This week thousands of reenactors, spectators and history buffs are returning to the fields around the once-remote railroad junction to remember the day the fledgling armies from North and South first met in 1861 — shadowed by picnickers, unaware of the dark future ahead.

Dozens of members of Congress went. Rep. Alfred Ely of New York, armed with a pistol, wound up captured by the rebels and was nearly shot by an enraged Confederate officer. Reporters, illustrators and a Union general’s father-in-law attended. A Rochester attorney went, was captured and later died in prison.

Mathew Brady, the vision-impaired photographer, put on a straw hat and long white “duster,” and went out in his equipment wagon with the British sketch artist Alfred R. Waud.

There were even a few vendors, hawking pies and snacks.

The site, amid fragrant grasslands baking in the heat 30 miles from Washington, was just southwest of a murky creek called Bull Run. It was quiet, gorgeous country with the hump of the Bull Run Mountains in the distance, tiny pink wildflowers in the fields and majestic turkey buzzards soaring on the thermals overhead.

The Union’s main general, Irvin McDowell, commanded a force of 35,000, probably the largest army ever assembled to that point in North America. The Southern force was slightly smaller, about 32,000.

Such a pageant, with some men in parade ground uniforms so gaudy one scholar says they resembled Robin Hood, could not be missed.

In the end, the battle of Bull Run — or Manassas as it’s often called in the South — became a bloody defeat for the Union. It turned out to be modest in size; a second battle over the same ground the following year involved much larger forces.

As for the pageantry, the event turned into a confused stampede of terrified politicians, picnickers, horses, wagons and defeated Union soldiers back to Washington.

Chaos had ruled the battlefield, as some Southern soldiers showed up in blue uniforms, some Northerners in gray, and the red-white-and-blue flags of both sides were almost impossible to tell apart.

And in the innocent summer of 1861, with a mysterious comet fading in the night sky, the name of the battle rang across the country and began filling newspapers with lists of the dead.

Among those killed would be Judge McCook’s young son, Charles, and about a thousand others.

“Now it seems that we are never out of the sound of the Dead March,” Southern diarist Mary Chesnut wrote from Richmond. “It comes and it comes and I feel inclined to close my ears and scream.”

But Bull Run was also the place where some of the war’s great figures took the stage.

There, the brilliant and eccentric Confederate Gen. Thomas J. Jackson got the nickname “Stonewall” for the stand made by his brigade.

And there, an untested Union commander, William T. Sherman, was grazed by one bullet, had another ruffle his coat collar, but survived to become one of the architects of Northern victory four years later.

Bull Run was also the field of shattered illusions, says historian Adam Goodheart: The one in the North that its mighty hosts would steamroll to Richmond, and the one in the South that its martial sons were more than a match for the “shopkeepers” of the North.

But it cemented the fractious Southern states, says historian William C. Davis. It gave them the victory on which to build a tradition of victory, however fleeting, and it guaranteed that there would be much more fighting.

Before all that, though, before the reality of war set in, the next-to-last weekend in July of 1861 was one of anticipation in Washington, the certainty of triumph and an eagerness to see the spectacle.

Russell, the veteran British military correspondent, was late getting started the morning of July 21, as his traveling companion from the legation got up late.

Russell recalled that it was a calm and quiet Sunday in Washington.

“I swallowed a cup of tea and and a morsel of bread,” he wrote later, “got a flask of light Bordeaux . . . a paper of sandwiches . . . and having replenished my small flask with brandy,” packed his rented two-wheeled carriage.

When he reached the Long Bridge over the Potomac River, a sentry said, “You’ll find plenty of congressmen on before you.”

The green, undisciplined Union army, urged into premature action by the newspapers and President Abraham Lincoln, had gone out several days before to dislodge the Confederates gathered at Manassas.

Now came the onlookers.

Among the politicians was Congressman Ely, armed with a borrowed pistol and headed to check on a regiment from his district. He had started before dawn in a large rented carriage in the company of Sen. Lafayette S. Foster, of Connecticut, and two other men.

En route they met Massachusetts congressmen Charles Delano and Alexander H. Rice, the former mayor of Boston; Ohio congressman John A. Gurley, and Massachusetts senator Wilson, with his sandwiches, all headed for the battle.

Ely’s entourage halted its carriage on a hill outside Centreville, a few miles east of Bull Run, amid “a great number of similar vehicles which had brought out many people from Washington, citizens, representatives and senators,” he wrote later.

Among those already in the vicinity was the eccentric former probate judge Daniel McCook, 63. He had headed out with a rifle and four more members of Congress, who planned to fight as volunteers beside their soldier constituents.

McCook met up with his son Charles, who had run away from prep school to join the Second Ohio infantry regiment and was on guard duty behind the lines.

The battle seemed to be going well for the Union and the two had lunch, along with other picnickers.

Glimpses of smoke could be seen in the distance, and the sound of heavy gunfire could be heard.

Russell, the reporter, was not far away. From his vantage point, he could see an excited Union officer on horseback crying, “We’ve whipped them on all points!” The bystanders cheered. The congressmen shook hands, and called out: “Bully for us! Bravo! Didn’t I tell you so?”

Russell, now on horseback himself, went forward to investigate. He had ridden about three miles when he encountered wagons hurrying past in the opposite direction. At first he thought they were returning for more ammunition, but then heard the drivers shouting, “Turn back! Turn back! We are whipped.”

The battle had at first gone well for the Union army, which had pressed in on the beleaguered Confederates all day. Then rebel reinforcements arrived. A Confederate counterattack unhinged the far right of the Yankee line, and the panic began.

Ely, unaware of developments, chose this moment to leave his carriage and proceed on foot. As he did, a bullet whistled by. He had just ducked behind a tree when an artillery shell crashed through the branches, “adding much to my alarm,” he wrote later.

Soldiers burst from nearby woods. Two officers approached Ely and asked who he was. When he answered, they took him prisoner. They were with the 8th South Carolina infantry regiment.

Ely was presented to Col. E.C.B. Cash, who pointed a pistol at the congressman’s head and said: “God damn your white livered soul! I’ll blow your brains out on the spot.”

Cash, a renowned hothead, was dissuaded by subordinates. But he later noted in his battle report that Ely “had come upon the field to enjoy the pleasure of witnessing our defeat.” Ely was held prisoner for five months.

Worse was to befall the McCooks.

Father and son had parted after lunch, and a Confederate cavalry charge caught the younger man unawares at his guard post, according to a history of the family by Charles and Barbara Whalen.

The younger McCook was mortally wounded just as his father returned.

Daniel McCook took his son in a carriage to a makeshift hospital in Fairfax, where the boy died early the next morning, reciting the old Latin text, Dulce et decorum est pro patria mori — “It is sweet and fitting to die for one’s country.”

McCook took the body to his house on Pennsylvania Avenue later that day.

“The carriage drove up to the door,” the Washington Evening Star recounted, “and was immediately surrounded by a crowd of persons whose sympathies were much excited by the distress exhibited by the family.”

It was “Black Monday,” as the New York diarist George Templeton Strong called the day after Bull Run.

No one knew that there would be many more such days over the next four years.