Year 100 was a leap year starting on Wednesday of the Julian

* Pliny the Younger advances to consulship.
* Tiberius Avidius Quietus' rule as governor of Roman Britain ends.
* Timgad (Thamugas) is founded by Emperor Trajan.
* Trajan creates a policy intended to restore the former economic supremacy of Italy.
* The Roman Army reaches 300,000 soldiers.
* Bricks become the primary building material in the Roman Empire.
* Lions have become extinct in the Balkans by this date.
* Pakores (last king of the Indo-Parthian Kingdom) takes the throne.
* The Kingdom of Himyarite is conquered by the Hadramaut.
* Paper is used by the general populace in China, starting around this year.
* The Hopewell culture begins in what is now Ohio circa this date.
* Teotihuacan, at the center of Mexico, reaches a population of 50,000.
* The Moche civilization emerges, and starts building an advanced society in present-day Peru.
* In China, the wheelbarrow makes its first appearance.
* The Temple of the God of Medicine is built in Anguo, China.
* The Fourth Buddhist Council is convened circa this year.
* Appearance of the first Christian dogma and formulas regarding morality.
* The compilation of the Kama sutra begins in India.