for St. Louis harbor and for the upper Mississippi and Missouri rivers. Among his projects was the mapping of the Des Moines Rapids on the Mississippi above Keokuk, Iowa, where the Mississippi's mean depth of was the upper limit of steamboat traffic on the river. His work there earned him a promotion to captain. Around 1842, Captain Robert E. Lee arrived as Fort Hamilton's post engineer. Marriage and family While Lee was stationed at Fort Monroe, he married Mary Anna Randolph Custis (1808–1873), great-granddaughter of Martha Washington by her first husband Daniel Parke Custis, and step-great-granddaughter of George Washington, the first president of the United States. Mary was the only surviving child of George Washington Parke Custis, George Washington's stepgrandson, and Mary Lee Fitzhugh Custis, daughter of William Fitzhugh and Ann Bolling Randolph. Robert and Mary married on June 30, 1831, at Arlington House, her parents' house just across the Potomac from Washington. The 3rd U.S. Artillery served as honor guard at the marriage. They eventually had seven children, three boys and four girls: George Washington Custis Lee (Custis, "Boo"); 1832–1913; served as major general in the Confederate Army and aide-de-camp to President Jefferson Davis, captured during the Battle of Sailor's Creek; unmarried Mary Custis Lee (Mary, "Daughter"); 1835–1918; unmarried William Henry Fitzhugh Lee ("Rooney"); 1837–1891; served as major general in the Confederate Army (cavalry); married twice; surviving children by second marriage Anne Carter Lee (Annie); June 18, 1839 – October 20, 1862; died of typhoid fever, unmarried Eleanor Agnes Lee (Agnes); 1841 – October 15, 1873; died of tuberculosis, unmarried Robert Edward Lee, Jr. (Rob); 1843–1914; served in the Confederate Army, first as a private in the Rockbridge Artillery, later as a Captain on the staff of his brother Rooney; married twice; surviving children by second marriage Mildred Childe Lee (Milly, "Precious Life"); 1846–1905; unmarried All the children survived him except for Annie, who died in 1862. They are all buried with their parents in the crypt of the University Chapel at Washington and Lee University in Lexington, Virginia. Lee is a great-great-great-grandson of William Randolph and a great-great-grandson of Richard Bland. Fitzhugh Lee (1835–1905), a Confederate general and later a United States Army general in the Spanish–American War, is Lee's nephew. Lee is a second cousin of Helen Keller's grandmother, and is a distant relative of Admiral Willis Augustus Lee. On May 1, 1864, General Lee was present