Wikipedia:Selected anniversaries/April 20
April 20: Ridván begins at sunset in the Bahá'í Faith, 4/20 in cannabis culture.
- 1653 - Oliver Cromwell dissolved the Rump Parliament of the Commonwealth of England.
- 1862 - Louis Pasteur (pictured) and Claude Bernard completed the first test on pasteurization.
- 1884 - Pope Leo XIII published the encyclical Humanum Genus, denouncing Freemasonry and the doctrine of a separation of church and state.
- 1914 - A fire and a gun battle between the National Guard and striking coal miners in Colorado led to 17 deaths in the Ludlow massacre.
- 1999 - Eric Harris and Dylan Klebold murdered 13 people before committing suicide in the Columbine High School massacre.