The building, designed by the famed architect Richard Neutra, was built in 1962, ahead of the battle's centennial anniversary, to house the 360-degree Cyclorama painting depicting Pickett's Charge.
But the building sits on Cemetery Ridge, where Union troops repelled Confederate forces led by Gen. George Pickett on the battle's final day, July 3, 1863.
Though reviled by Civil War buffs, who have long believed it has no place on the 19th-century battleground, the concrete circular structure is at the same time beloved by fans of Modern architecture.
The park service first announced its intention to demolish the building in 1999. But a group of preservationists seeking to save the structure - which by virtue of its age and design is eligible for the National Register of Historic Places - won a court victory in 2010 that forestalled the demolition.
The U.S. District Court for the District of Columbia directed the park service to conduct an environmental analysis on the demolition and to consider "non-demolition alternatives" such as moving the structure or leaving part of it intact.
Lawhon said Thursday that the park service had determined that there was no need for the continued use of the building, and that retaining it conflicted with the overall goals and purpose of the park to preserve the battlefield.
"The site is a key portion of the Union battle line and is important to the public understanding of what happened here," Lawhon said. "The Cyclorama building was a disruption to that."
Informed of the demolition news, Cyclorama supporters contended that park service officials were abrogating their role as stewards of the recent past, and said the agency was engaging in "revisionist history" by destroying the building.
"That will result in the loss of a legitimately historic structure, ultimately eroding the overall historic integrity and fabric of Gettysburg," wrote Alan Higgins, president of the Recent Past Preservation Network in an e-mail.
The private Gettysburg Foundation will cover the $3.8 million demolition cost.
The 12-ton, 27-foot-high, 377-foot-long canvas depicting Pickett's Charge is now on display in the park's visitor center.
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