In the summer of 1794, as French Republican troops approached Antwerp, Flemish aristocrat Henri Joseph Stier and his family fled to Philadelphia with their most valuable possessions, including the finest collection of Old World master paintings ever to cross the Atlantic at that time. The family moved to Annapolis in 1795, where Rosalie Stier met George Calvert, a delegate to the Maryland Legislature and grandson of the fifth Lord Baltimore. They married in the summer of 1799, spent part of their honeymoon at Mount Vernon, and lived at Mount Albion near Upper Marlboro. In 1800, Henri Stier bought farmland near the port of Bladensburg and began building a plantation house. He and his wife moved into the east wing in 1802, and in 1803 the Stier family, except for Rosalie, returned to Antwerp under an amnesty. Rosalie and George Calvert then took over the still unfinished house, by then called Riversdale, completed it by 1807, raised their children there, and spent the rest of their lives there. Rosalie's letters to her family, later published in Mistress of Riversdale, provide an intimate picture of upper-class family life near the Federal City in the early republic and helped guide the mansion's restoration. The painting collection remained at Riversdale until 1816, when it was returned to Antwerp, and the works later entered museums and private collections around the world. In 1838, Riversdale passed to Rosalie and George Calvert's second son, Charles Benedict Calvert, a U.S. congressman, progressive farmer, and principal founder of the Maryland Agricultural College, now the University of Maryland at College Park. His heirs sold Riversdale and about 450 acres in 1887 to a New York firm that developed the planned railroad suburb of Riverdale Park. Over the next 50 years the house had a series of private owners. In the late 1940s, retired U.S. Congressman Abraham Lafferty sold the house and its remaining grounds to the Maryland-National Capital Park and Planning Commission, which used Riversdale as offices until restoration began in 1988. Riversdale reopened to the public in 1993 and became a National Historic Landmark in 1997.