History is written by the victors, the saying goes. One of the main themes of Thomas A. Desjardin's eye-opening book about Gettysburg is that history is also written by the petty, the vindictive, the confused, the forgetful, the careless, the boastful, the sycophantic, the glory-seeking, the blame-ascribing and the credit-grabbing.

People representing all of those characteristics, and more, wrote the history of Gettysburg. They so built up the importance of the battle as a watershed event in American history that many of us have come to believe that we know a great deal about what happened there and its significance to the outcome of the Civil War. Now along comes Desjardin to painstakingly show that much of what we have come to believe is wrong.

In the introduction, he sums it up: "The truth about Gettysburg is buried beneath layer upon layer of flawed human memory and our attempts to fashion our past into something that makes our present a little easier to live in. . . . Having done this, we revere the story and the place, passing it on to the next generation with our new adornments while sending to the future an image of the past to read and learn from. We create mythology."

In the case of Gettysburg, lots of people - from the serious to the seriously weird - helped shape the public's view of the battle. Union General Daniel Sickles was one. He was the first American ever acquitted of murder by reason of temporary insanity and was once charitably described as "one of the bigger bubbles in the scum of the legal profession, swollen and windy, and puffed out with fetid gas."

Sickles disobeyed orders at Gettysburg, creating a near-catastrophe for the Union. Wounded, Sickles was sent to convalesce in Washington, where he pre-emptively sought to deflect criticism of his own failures by blaming commanding General George Meade. Among others, information-hungry President Lincoln hung on every word.

Another who helped to form public perceptions (or misperceptions) about Gettysburg was a landscape artist named John Bachelder. Bachelder, who failed to capitalize on a painting depicting the battle of Bunker Hill, decided he would do a similar painting of the decisive battle of the Civil War, and he asked friends in the Union army to summon him whenever that occurred. If history didn't agree that Gettysburg was the greatest battle, Bachelder's painting would be similarly discounted. "So," Desjardin writes, "Bachelder became a sort of cheerleader in chief for the idea that this was the deciding event of the war. Through his own tireless efforts at promotion, a landscape painter from New Hampshire striving to prove himself right took his place as the most important of all Gettysburg historians and had a profound effect on virtually anything ever written about it afterward."

Southerners were equally active in trying to promote their interpretation of events, none more so than General Jubal Early, who tirelessly sought to blame the loss of the battle on General James Longstreet. According to Early, Longstreet failed to follow the so-called "sunrise attack order" that would have sent Pickett's soldiers into the Union lines much earlier on the final day of the battle, and, presumably, to victory instead of defeat.

This interpretation served Early's dual purposes of absolving Robert E. Lee of blame and of furthering the overall notion that the South lost the battle more because of what it did wrong than what the North did right. Inconveniently for Early, no evidence for such an order exists.

But while some used the battle to disparage, others used it to glorify. Helped by non-historians, including Ted Turner and Ken Burns, Union officer Joshua Lawrence Chamberlain has become the hero of Gettysburg, the professor-turned-soldier who almost single-handedly saved the Union from disaster. Most of what has been written about Chamberlain has as its original source an account written by Private Theodore Gerrish of Chamberlain's 20th Maine. Yet it turns out that much of what Gerrish presented as fact was little more than speculation: During the critical battle that elevated Chamberlain to hero status, Gerrish was in a hospital in Philadelphia. This hasn't stopped subsequent writers from building their books on Gerrish's shaky foundation.

The legend of Gettysburg is full of stories like this. Desjardin, a historian for the National Park Service in Gettysburg and a Ph.D. in American history, takes care not only to explain what myths there are, but also how they came to be. You leave These Honored Dead knowing that we may never know the truth about Gettysburg, but at least now we know some of the fiction.

And we know, as well, that the truth is a malleable force, and that, as Faulkner said, "History isn't dead, it isn't even past."

Dan Danbom is a free-lance writer living in Denver.