Authorities said they found the Eternal Light Peace Memorial adorned with spray-painted obscenities and symbols last week, WGAL-TV, Lancaster, Pa., reported Wednesday.
The exact nature of the graffiti was not reported, but the TV station confirmed the vandals' work had been covered up with boards.
Park officials said the boards became necessary after graffiti removal attempts on Tuesday failed.
Officials said it could cost thousands of dollars to repair the damaged U.S. Civil War memorial, WGAL reported.
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