The 9th century is the period from 801 to 900 in accordance with the Julian calendar in the Common Era.
- An unknown event causes the decline of the Maya civilization.
- Large-scale Viking attacks on Europe begin, killing countless numbers of people.
- The Magyars begin their conquest of Pannonia (roughly modern day Hungary), a process that will take several decades to be completed.
- In Italy, some cities became free republics.
- 802: Jayavarman II of the Khmer people in Cambodia founds the Khmer Empire and establishes the Angkorian dynasty.
- 803: Construction on the Leshan Giant Buddha in Tang Dynasty China is complete, after 90 years of rock-carving on a massive cliff-side.
- 805 - 820: Tang Dynasty was under the rule of Emperor Xianzong of Tang.