On the night of June 1, 1861, a scouting party of Virginia militia attacked U.S. troops at Arlington Mill. Company E of the 1st Michigan Volunteer Infantry Regiment was on picket duty at the mill guarding the Columbia Turnpike and the Alexandria, Loudoun, and Hampshire Railroad, while in a nearby house Company G of the 11th New York Volunteer Infantry Regiment, the 1st New York Fire Zouaves, prepared to relieve them. At about 11 P.M., the Virginians fired at the pickets, killing one and wounding another. After a brief exchange of fire, the militiamen were driven off with one man wounded. This skirmish was among the first military engagements of the Civil War. It took place only a week after the May 23 vote ratifying Virginia's secession from the United States. The next day, President Abraham Lincoln ordered Union forces to cross the Potomac River and occupy Arlington Heights. The fight helped show that Washington was vulnerable to Confederate attacks and that its defenses needed to be strengthened.