RICHMOND, Va. (AP) — In the PBS American Experience documentary "Death and the Civil War" premiering Tuesday night, bloated Union and Confederate bodies are shown scattered on battlefields and in trenches and bleached skulls and body parts are stacked like cordwood.

As the title suggests, death is the central theme of this moving, extraordinarily graphic film based on Harvard University President Drew Gilpin Faust's acclaimed book "This Republic of Suffering."

It chronicles how utterly unprepared a divided nation was for the mountains of dead the Civil War would produce and how that experience forever changed the way the country treats the men and women who give their lives for their nation.

"No one thought that this was going to go on this long. No one thought there would be deaths on this scale," Faust said in an interview with The Associated Press. "I think the South was stunned that the North didn't just let them go."

The war dead were left to rot where they lay mortally wounded. There was no ambulance corps to retrieve the dead or national cemeteries like Arlington in which to bury them.

On the home front, mothers and fathers, wives and girlfriends often never learned the fate of their loved ones. There was no system to identify the dead or notify families, or recompense for their loss.

To this day, the precise number of Civil War dead remains elusive, with the estimated toll increasing to 750,000 based on the research of J. David Hacker, a demographic historian at Binghamton University in upstate New York. That number, cited by the documentary and a growing number of historians, is much higher than the 600,000 that had been cited for decades. Some believe it may be as high as 850,000.

"Death and the Civil War," produced and directed by multi-Emmy Award-winning filmmaker Ric Burns, will air for two hours on the 150th anniversary of Antietam — the single bloodiest day on U.S. soil. The film draws heavily on historic battlefield photographs, the narrative of historians and the words of soldiers in letters home. It also includes the commentary of poet-undertaker Thomas Lynch and Joint Chiefs Chairman Mike Mullen.

The film opens with a reading of the bloodstained letter from Confederate Pvt. James Robert Montgomery, 26, to his father in Camden, Miss., after the younger Montgomery lay dying from a terrible shoulder wound.

"Dear Father, this is my last letter to you," Montgomery writes. "I am very weak but I write to you because I know you would be delighted to read a word from your dying son."

Faust is intimately familiar with the Civil War and its legacy of death. Her parents are buried in a graveyard that contains the remains of Confederate soldiers under unmarked stones.

"So in a sense, the subject of this book was right before my eyes," she said.

It was her research on Southern slave-holding women that piqued her interest in the inescapable fact of the Civil War: its staggering death toll.

"As I was reading letters from these Civil War women, they were just writing about death all the time," Faust said. "They were either anticipating it or mourning their dead or trying to recover and continue to their lives, so I thought this is something that needs to be looked at specifically."

"Death and the Civil War" does that in detail, presenting photograph after photograph of the dead on battlefields from the Deep South to Gettysburg.

"What did they do with all those bodies?" Faust wondered. "What did that mean for families? How did people mourn and how did that change."

As for the bodies, little was done. Hundreds of thousands were left to rot where they fell. Wild hogs rooted through the remains. At Gettysburg, the stench of death from bodies never buried lingered months after the midsummer battle, forcing residents to cloak the odor with peppermint oil on their faces into the fall.

Burns, who produced the seminal series "The Civil War" with his brother Ken, has pored through hundreds of thousands of historic images from the Museum of the Confederacy in Richmond, the Library of Congress and other sources through the years. He said every "government institution in place to deal with death was shattered and transformed" by the unprecedented deaths of the Civil War.

"How profoundly unprepared we were," he said. "No one thought a war could mean mayhem on that scale. We were always one step behind when it came to death in the Civil War."

"Death and the Civil War" does much more than catalog the death. It also tells the often heroic and inspiring stories of people who were appalled by the carnage and were inspired to act. Their actions were transformative and live on today.

Red Cross founder Clara Barton, then 39 and a clerk in the U.S. Patent Office, saw battle wounds being wrapped with corn husks. She lobbied the Union Army to deliver medical supplies to the injured.

Dr. Henry Bowditch, a Boston physician, was told his son was injured in battle only to discover upon his arrival in Washington, D.C., that he had died. He later became an avid advocate of battlefield ambulance services.

Edmund Burke Whitman who, as superintendent of national cemeteries after the war, ambitiously scoured battlefields to retrieve and properly bury hundreds of thousands of soldiers in national cemeteries. He recovered 40,000 bodies between Natchez and Vicksburg, Miss., alone, a distance of 80 miles.

"One of the aspects of doing this project that was most meaningful to me," Faust said, "was seeing how individuals wanted to resist the inhumanity that was introduced into the world in which they lived and how they really wanted to affirm what it meant to be human — how you treat the dead, how you remember the dead."

In the end, she said, "I thought it was a really affirmative story."