MANASSAS, Va.-Sesquicentennial, a long word, fits the commemoration of a war that began 150 years ago and produced the greatest number of American casualties in any war. About 620,000 Americans in a population of 30 million died. The equivalent today, in our population of 309 million, would be 6 million dead.

The tragedy began with celebration in Charleston, S.C. Last month, on April 12, several hundred persons gathered in that city before dawn, much as their predecessors had assembled in 1861 to view the start of a bombardment of Fort Sumter just offshore. But in the commemoration, at 4:30 a.m., the time the first shots were fired, a brass ensemble began a concert titled "When Jesus Wept."

Later that day, an African-American reenactor, dressed in a uniform of the 54th Massachusetts Volunteer Infantry, the regiment of black troops that tried to capture another harbor fort in 1863, threw a wreath into the sea. The mass grave into which Confederates threw the unsuccessful assailants no longer exists, and Atlantic hurricanes have washed the corpses out to sea. (The fine 1989 movie Glory memorializes the attack.)

The sesquicentennial's next bittersweet look back will come at Manassas National Battlefield Park in Virginia on July 21. (See Andrée Seu's column for the lovely words of a soldier who died there.) I walked the battlefield's gentle slopes last month, for the first time in 20 years, and saw that its defenders had successfully fought off threats from shopping malls and residential development.

Those who visit the battlefield in July will encounter four days of planned Manassas anniversary events that include opening and closing orations: In between, numerous musketry and artillery firing demonstrations will alternate with a variety of guided tours. Children with imagination will still be able to run up Henry Hill and pretend to be arriving on the scene like Gen. Thomas L. Jackson, about whom Gen. Barnard Bee shouted, "There stands Jackson like a stone wall! Rally behind the Virginians!"

In 1861 other Southern soldiers did rally behind the Virginians. Soon, U.S. congressmen with picnic baskets, who had carriaged out from the Capitol to watch what they thought would be a colorful, war-ending show alongside a little river called Bull Run, were racing back to Washington, followed by panicky soldiers. Some Southerners thought their victory would end the war. Both side's prophets of easy wins were wrong: The war ground on until 1865, producing more misery each year.

But it also produced great battlefields to visit. On many it's still possible to get the lay of the land on foot, walking the way the armies walked. Here are six of my favorites:

Shiloh • April 1862

A small country church still meets at the spot where Southern forces on an early Sunday morning attacked U.S. Grant's army. The Tennessee battlefield's markings make it easy to follow the course of savage fighting over two days that produced 25,000 casualties. Some of the dead were buried in mass trenches that are still well-marked. The general praised as the South's best, Albert Sydney Johnston, ordered his staff physician to attend a group of Federal wounded-and then bled to death when a bullet severed his femoral artery. ("These men were our enemies a moment ago," Johnston had told his doctor, who had not wanted to leave. "They are our prisoners now. Take care of them.")

Antietam • September 1862

Neither side could gain the advantage in this one-day battle that produced 23,000 casualties. A farm road worn down by erosion and called Sunken Road-until it gained a new name at the battle, Bloody Lane-is a good place to meditate on man's sin. Another part of the battlefield is a monument to stupidity. Union general Ambrose Burnside hour after hour added to the casualty figures by sending men across a heavily defended bridge across Antietam Creek. Yet, as the war's best historian, Shelby Foote, writes, "The little copper-colored stream, less than fifty feet in width, could have been waded at almost any point without wetting the armpits of the shortest man in his corps."

Fredericksburg • December 1862

The stonewall at Marye's Heights stands as another reminder of the general who gave us the word sideburns. Burnside sent Northern troops uphill across 400 yards of open Virginia terrain. Those who survived the fire of massed artillery ran into the massed fire of Confederate riflemen behind the wall. About 8,000 Union soldiers died or were wounded. Not one reached the wall. Burnside, distraught by his deadly decisions, wanted to lead a new assault personally the next morning, but others dissuaded him. The armies remained in a standoff for two days, while Union soldiers froze to death on the acres between the armies.

Chancellorsville • April 1863

Driving and walking the tree-shaded route of Stonewall Jackson's flank attack will allow you to grasp the war's purest example of bold tactical brilliance. Northern forces outnumbered the confederates 130,000 to 60,000, more than two to one, but Lee and Jackson divided their small force, with Jackson hurrying 30,000 infantrymen on a 12-mile march around Hooker's army. The Confederates came out of the Virginia underbrush screaming the Rebel yell-and the rout was on, until darkness fell. Then Jackson fell, shot by his own men in the confusion. He died eight days later. The North had 17,000 casualties, the South 12,800.

Gettysburg • July 1863

Gettysburg was the single greatest battle of the war, stretching over three days and involving 170,000 men, with over 23,000 Union soldiers and 28,000 Confederates becoming casualties. Driving and walking this Pennsylvania battlefield explains much: The big rocks of Devil's Den were indeed devilish, and the awesome difficulty of "Pickett's Charge"-across a vast expanse, sloping slightly uphill-makes it seem that Robert E. Lee's hope that day was for God to intervene. (That's what Michael Shaara suggested in his fine novel, The Killer Angels; it's well worth reading before a Gettysburg visit.) Some Union soldiers who shot down the hapless Confederates yelled, "Fredericksburg! Fredericksburg!"

Cold Harbor • June 1864

By 1864 Abraham Lincoln and his generals had settled on a war of attrition: "doing the arithmetic," Lincoln called it, for the North could lose men and replace them, but Southern forces that lost half as many remained depleted. On the night before battle, all through the lines, Northern soldiers stirred to scrawl their names and home addresses on slips of paper and pin them to the backs of their coats: That way their corpses the next day could be identified more readily. U.S. Grant's forces at Cold Harbor, Virginia, had 7,000 casualties, most of them during a furious 8­minute assault against the Southern lines. Robert E. Lee's army lost 1,500. One blood-stained diary found in the pocket of a dead Northern soldier had this final entry: "June 3. Cold Harbor. I was killed."