On September 30, 1889, the first building of the Mayo Clinic opened to the public. The Mayo Clinic evolved in stages. Its history can be traced back to the Civil War, when William Worrall Mayo was made an examining surgeon for the military draft board in 1863 and sent to Rochester, Minnesota. He liked the town so much he decided to stay and invited his wife and two sons to come live there with him. Then 20 years later, in 1883, a tornado struck Rochester, Minnesota, killing 24 people and injuring more than 40. William Mayo and his sons, Will and Charlie, worked with Mother Alfred Moes and the Sisters of St. Francis to set up a makeshift hospital to treat the wounded.