On Twitter the Library of Congress has retweeted this morsel from the WorldDigitalLibrary: "Battle of #Antietam was #OnThisDay in 1862. 23,000 killed. ..."
The Libraryof Congress should know better. The butcher's bill* for Antietam, the 23,000, is the number of casualties. The number of dead, Union and Confederate combined, in the bloodiest day in U.S. military history, was 3,650; wounded, over 17,000; missing or captured, nearly 1,800.
*The mordant nineteenth-century term, often attributed to Admiral Lord Nelson, for the human costs of a battle.