In 1862 Island No. 10, so named because it was the tenth island south of the junction of the Ohio River with the Mississippi River at Cairo, Illinois, was a natural fortress approximately 1 mile long and 450 yards wide, sitting at about 10 ft above low water in the middle of the channel and straddling the boundaries of the states of Tennessee, Missouri, and Kentucky. It was an ideal site from which Confederates could maintain control of the rivers to the West. But in March and early April of that year, the combined Union army and navy launched a campaign for command of Island No. 10, which became the site of the first extensive siege of the Civil War.