|Centuries:||3rd century – 4th century – 5th century|
|Decades:||270s 280s 290s – 300s – 310s 320s 330s|
|Years:||300 301 302 – 303 – 304 305 306|
- Great Persecution: Emperor Diocletian launches the last major persecution of Christians in the Empire. Hierocles is said to have started the fierce persecution of the Christians under Galerius. They are forbidden to worship in groups, and thousands of them are killed in the next 10 years.
- February 24 – Galerius publishes his edict that begins the persecution of Christians in his portion of the Empire.
- September 25 – On a voyage preaching the gospel, Saint Fermin of Pamplona is beheaded in Amiens, France.
- November 28 – Diocletian makes a visit to Rome. The Augusti and the Caesars are united for the first time to celebrate the 20th anniversary of Diocletian's accession.
- The Triumphal Arch of Maximian is erected in Salonica.
- April 23 – Saint George, soldier of the Roman Empire
- September 25 – Saint Fermin, Roman Catholic saint
- Acacius of Byzantium, centurion in the Roman army and martyr
- Adrian of Nicomedia, Christian saint
- Anthimus of Rome
- Cao Huan, last emperor of the Kingdom of Wei
- Cessianus, Roman Catholic saint and martyr
- Crescentinus, patron saint of Urbino
- Erasmus of Formiae
- Expeditus, Roman commander and martyr
- Felix and Adauctus, Christian martyrs
- Lu Ji, Chinese writer and literary critic
- Romanus of Caesarea, martyr
- Saint Cyriacus
- Saint Devota
- Saint Pantaleon
- Victor Maurus, Christian martyr
- Vitus, Christian saint from Sicily