Horwitz, who won a Pulitzer Prize with The Wall Street Journal before becoming an author of historical non-fiction, died suddenly in Washington while touring for his latest book.

His publisher, Penguin Press, said Horwitz had died on Monday of an apparent heart attack.

As a Wall Street Journal reporter, Horwitz won the 1995 Pulitzer Prize for national reporting for stories he wrote about income inequality and working conditions in low-wage America.

His national bestseller “Confederates in the Attic” about the men and women who re-enact battles from the 1861-65 Civil War was published in 1998.

Horwitz’ latest book, “Spying on the South: An Odyssey Across the American Divide,” about the 1850s travels of landscape architect Frederick Law Olmsted – designer of New York’s Central Park – was published this month.

Among his other works were “Midnight Rising” about the pre-Civil War abolitionist John Brown and “Blue Latitudes” about Captain James Cook.

A native of Washington, Horwitz, who was married to Geraldine Brooks, also a successful novelist, lived in Martha’s Vineyard in Massachusetts.