Year 900 (CM) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar.
|Centuries:||8th century – 9th century – 10th century|
|Decades:||870s 880s 890s – 900s – 910s 920s 930s|
|Years:||897 898 899 – 900 – 901 902 903|
- Persian scientist, Rhazes, distinguished smallpox from measles in the course of his writings. Holding against any sort of orthodoxy, particularly Aristotle's physics, he maintained "the conception of an 'absolute' time, regarded by him as a never-ending flow".
- Gyeonhwon formally establishes the kingdom of Hubaekje in southwestern Korea.
- Merchants from southwest Asia and India settle on the east-African coast, trading gold, beads and metal for ivory and slaves.
- Harold I of the Yngling or Scilfing dynasty subdues the petty kings of Norway and conquers the Orkney and Shetland islands.