Shapur I became co-emperor of the Sasanian Empire with his father Ardashir I.
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Jonas Salk's Polio vaccine tested by Jonas Salk was given final approval by the US Food and Drug Administration.
Hillary Clinton announced her candidacy for US President.
Israeli Knesset chose April 13 as the official Holocaust Remembrance Day.
The Battle of Fort Sumter in South Carolina between the United States and the Confederate States started the American Civil War.
Rock Around The Clock by Bill Haley and His Comets was recorded.
