SHARPSBURG, MD. -- As a boy, Derek Cristroamed Antietam National Battlefield on the outskirts of town, itsrolling hills and gentle streams a child's dream playground.

In2010, Army Sgt. Crist returned home from two tours in Afghanistan,where nearly 2,000 American servicemembers have died. His platoon losttwo soldiers. He says he had not thought deeply about the history of hishometown until he saw fellow soldiers killed and wounded. The groundwhere, 150 years ago Monday, more than 23,000 were killed, wounded orwent missing in the bloodiest day of combat in American history isindescribably more personal.

"The loss of onefriend is pretty rough," says Crist, 25, who is out of the Army andpursuing a business degree. "And then you realize you had all that goingon right here."

Antietam is a gash in historythat is still healing. But it also has become a place of learning, andnot just for young military officers studying tactics. As the residentsof Sharpsburg and surrounding communities learned long ago -- and asmany Americans know from Afghanistan and Iraq -- war's aftershocks echolong after the last shots are fired.

Besidesstopping Robert E. Lee's first invasion of the North and giving AbrahamLincoln the ability to issue the Emancipation Proclamation after abattlefield success, Antietam was the site of major advances inbattlefield medicine that are being studied and used in Afghanistan.

Asthe long wars in Iraq and Afghanistan move into history, an aftermathcommences -- in the memories of the fallen and in the challenges of theinjured and their families.

Gettysburg willbe remembered on its sesquicentennial next year as the turning point inthe Civil War. By comparison, Antietam is tucked away in the historybooks. But arguably its legacy is as powerful, its aftermath equallypoignant. On this 150th anniversary, stories are retold about familieshiding in neighbors' basements; of recovering and dying soldiers nursedin homes or churches for weeks; of diaries describing the smell andsounds of armies hurrying toward battle and limping away afterward.

Evenin a war marked by seemingly endless casualty lists, the 12 hoursaround Sharpsburg and Antietam Creek stand alone. Tactical blunders,miscommunication, geography and individual heroism conspired to create atableau of up-close killing so horrific that for decades thereafter,legions of veterans returned to sort through what they had survived.

Sharpsburg'sannual Memorial Day parade dates to 1867, when North and Southveterans began returning. Last year, Crist and other Iraq andAfghanistan vets had a place of honor.

Theparade draws people from afar, swells the town and is populated bywaving soldiers. That is precisely what happened to Sharpsburg on Sept.17, 1862.

Modern battlefield medicine

Antietam has become more than just the memory of a single day.Techniques first applied here by Jonathan Letterman, the Union Army'smedical director, were the basis of modern battlefield medicine and ablueprint for today's civilian emergency response system.

AtAntietam, Letterman first tried a coordinated, progressive system oftrained first responders, triage stations, surgical field units andpermanent hospitals. For civilians today, that's ambulances with EMTs,emergency rooms, operating rooms and hospital room convalescence.

"Everytime you see an ambulance run down the road as a result of a 911 call,that is the Battle of Antietam going down the road in front of you,"says George Wunderlich, executive director of the National Museum ofCivil War Medicine in nearby Frederick, Md.

Since2004, Wunderlich's non-profit Letterman Institute has had classes atAntietam for roughly 5,000 doctors, nurses, medics and other U.S.military medical personnel.

They walk the24-acre Cornfield, which changed hands six times and left dead andwounded in heaps. They stop for lectures at Bloody Lane, where 5,600were mowed down in three hours along an 800-yard road. They can walk inseconds across Burnside Bridge, a narrow stone arch over Antietam Creekthat 150 years ago cost blue-clad Yankees three hours and 500casualties to cross.

Wunderlich says that ateach stop, "we lay out how many wounded are in this part of thebattlefield. We make them think in terms of how you would do this jobtoday."

He says physicians have studied bonesfrom wounded Civil War soldiers because roadside bomb injuries in Iraqand Afghanistan are similar to those from cannon fire at Antietam.

Lt.Col. Justin Woodson, an emergency physician for the Uniformed ServicesUniversity's Military and Emergency Medicine Department, lectures on anannual trip to Antietam for all first-year military medical students.Woodson, who served in Iraq, traces medical decisions from the point ofinjury to stretcher, ambulance, field hospitals and more permanentfacilities as far away as Frederick, 22 miles from the battlefield.

"We do the same thing on a modern battlefield," Woodson says.

War 'was not a lark'

Inhistory's broad brush, Antietam was a military draw but a strategicNorthern victory. Shortly thereafter, Lincoln issued the EmancipationProclamation ending slavery.

The battle movedthe Civil War "beyond reunion (of the states) to freeing 4 millionpeople," says Susan Trail, superintendent of Antietam NationalBattlefield. "It was just a horrific battle. People by this time in thewar were starting to realize this was not a lark."

Despiteits proximity to history, Sharpsburg has resisted commercialization.The population is smaller today than in 1862. Developers have beenshooed away for 150 years. Some buildings at the time of the battle areimmaculately kept and commemorated with plaques. Others are abandoned orfalling down.

"We like it to be just a small,quiet town," says Mayor Hal Spielman, who is descended from the familyof Joseph Poffenberger, whose farm was a vital staging area and hospitalfor Union troops. It's also near where Red Cross founder Clara Bartonbecame famous for treating the wounded.

A2-foot-wide cannonball crevice remains in a prominent Main Street home.Poffenbergers today attend the Christ Reformed Church on Main Street,which still has blood marks on the floor and two stained-glass windowsdedicated to the wounded boys of Connecticut regiments hospitalizedthere.

Wunderlich says some around Sharpsburgand neighboring towns still know where their families hid during thebattle or which units camped on their property.

"They can tell you everything about the battle as if it happened to them," he says.

Inexplicable carnage

BillPoffenberger, 78, says he's never understood why the Yankees neverforded the Antietam Creek that he would easily wade across as a boy. Hewill never know, he says, what was "in a man" that could make him runinto certain death or wounding at Burnside's Bridge or how the men onthe other side could keep killing.

"Those were 23,000 brothers out there," Poffenberger says of the fallen.

Bob Kozak first came here from Ohio with his father in 1967. Kozak sayshis dad, who fought in the Pacific in World War II, stopped at BloodyLane and said, "This was no battle. This was murder."

Kozak,who lives in Frederick, commemorates the sesquicentennial byre-creating Alexander Gardner's controversial photographic exhibit, "TheDead Of Antietam."

The black-and-whites ofdead men and horses and shattered equipment sprawled across the fieldswas shown in New York City three weeks after the battle. Kozak says hisre-creation "brings the story forward, to our doorsteps."

Shocking for a public that had never seen battlefield deaths before,Gardner's exhibit spurred debate over war censorship that echoes today,from what embedded journalists should show of combat to whetherreturning coffins from Iraq and Afghanistan should be photographed.

Theexhibit will open Oct. 5 at the battlefield's Pry House, itselfsymbolic of Antietam's ripples. The Pry farm was Union Gen. GeorgeMcClellan's headquarters during the battle. The house and barn werehospitals for 400 soldiers and officers. The Pry family never recoveredfull damages and eventually moved to Tennessee.

Daysafter the battle, Lincoln visited the wounded Gen. Israel Richardson atthe Pry home. Richardson lingered upstairs for six weeks before dying,cared for by his wife and sister who had traveled from Michigan. Theytook him home for burial. They were among scores of family members whocame looking for loved ones, including the father of eventual SupremeCourt Justice Oliver Wendell Holmes Jr., who was critically wounded .

EachDecember, volunteers scatter 23,000 burning candles across thebattlefield. Trail says the volume is overwhelming, even more when shethinks of those affected by each loss. She draws parallels to today, to"soldiers being away from home, people being wounded and having toadjust their lives."

"These people 150 yearsago weren't any different," Trail says. "They had the same needs, thesame family lives, dreams and aspirations. And so it is important for usto not just have statistics and numbers in a book."