3h 45min, may 24, 1861 y - Union forces cross the Potomac River and occupy Arlington Heights, the home of future Confederate General Robert E. Lee. It is during the occupation of nearby Alexandria that Colonel Elmer Ellsworth, commander of the 11th New York Infantry and a close friend of the Lincolns, is shot dead by the owner of the Marshall House just after removing a Confederate flag from its roof. (Timeline)