The event, which is put on by the Gettysburg Anniversary Committee, will cost about $1 million and will stretch from Thursday to July 7, The (Philadelphia) Inquirer reported.
Jon Sirlin, a Philadelphia lawyer who acts as a Union officer and chief of staff, said it's easy to forget your real life when in the middle of such bloodless battles.
"It's extremely accurate and feels real -- the noise, conditions, and spectacle -- but you're not confronting the likelihood of you or your friends being killed," he said.
Another, smaller, reenactment battle is being held through Sunday at the Bushey Farm on Pumping Station Road, held by the Blue Gray Alliance.
The major Gettysburg battle is expected to draw up to 80,000 spectators.