At about 2 a.m. on Dec. 16, 1811, the ground began to shake uncontrollably. Large trees throughout Missouri, Kentucky, Arkansas, Tennessee, Illinois and other states swayed, then snapped. Steep bluffs tumbled into the Mississippi River, which overflowed its banks and appeared to flow backward in places. Cracks in the ground appeared, some of them miles long and wide enough to swallow livestock. Black rocks as heavy as 30 pounds shot into the air through holes that instantaneously developed in the ground.