|Centuries:||2nd century – 3rd century – 4th century|
|Decades:||270s 280s 290s – 300s – 310s 320s 330s|
|Years:||297 298 299 – 300 – 301 302 303|
|300 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1053|
|Chinese calendar||己未年 (Earth Goat)
2996 or 2936
— to —
庚申年 (Metal Monkey)
2997 or 2937
|- Vikram Samvat||356–357|
|- Shaka Samvat||222–223|
|- Kali Yuga||3401–3402|
|Iranian calendar||322 BP – 321 BP|
|Islamic calendar||332 BH – 331 BH|
|Minguo calendar||1612 before ROC
|Seleucid era||611/612 AG|
|Thai solar calendar||842–843|
Year 300 (CCC) was a leap year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Valerius (or, less frequently, year 1053 Ab urbe condita). The denomination 300 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- The Franks penetrated into what is now northern Belgium (approximate date).
- The city of Split is built.
- Camp of Diocletian is built in Palmyra.
- A Romano-Celtic temple-mausoleum complex is constructed in what is now Lullingstone, and also in Anderitum (approximate date).
- The lion becomes extinct from Armenia (approximate date).
- The Yayoi period ends in Ancient Japan (approximate date).
- Wootz steel is developed in India (approximate date).
- The Kama Sutra, an Indian handbook on the art of sexual love, is probably produced around this time by the sage Vatsyayana.
- The elephant becomes extinct in North Africa (approximate date).
- The Atlas Wild Ass becomes extinct (approximate date).
- The Formative/Preclassic period in Mesoamerica comes to an end (around this year).
- The Mayan civilization reaches its most prolific period, the classic period, in what is now Guatemala, Belize and parts of southern Mexico adjacent to the former two. During most of this period, Tikal dominates the Mayan world.
Arts and sciences
- The magnetic compass for navigation is invented in China (approximate date).
- The Panchatantra, a Sanskrit collection of fables and fairy tales, is written in India.
- The Tetrarchs are probably made in Egypt. After 330 they are moved to Constantinople and in 1204 they are installed at the corner of the facade of the St Mark's Basilica, Venice (approximate date).
- Diocletian's Palace, Split, Croatia, is built. Its model is nowadays kept at the Museo della Civilta Romana, Rome.
- Peter of Alexandria becomes Patriarch of Alexandria.
- Possible date of the Codex Vaticanus Graecus 1209 and Codex Sinaiticus, manuscripts of the Bible written in Greek.
- Tiridates III makes his kingdom of Armenia the first state to adopt Christianity as its official religion.
- Approximate date of the Synod of Elvira in Elvira, Spain, which was a church council that prohibited interaction with Jews, pagans, and heretics.
- Asanga, founder of the Yogacara of Mahayana Buddhism (approximate date)
- Frumentius, Syrian Christian trader (approximate date)
- Hilary of Poitiers (approximate date)
- Li Shou, emperor of Cheng Han (d. 343)
- Jin Mindi, emperor of the Jin Dynasty (d. 318)
- Macarius of Egypt, Christian hermit and monk (approximate date)
- Zeno of Verona, Bishop of Verona and martyr (approximate date)
- Jia Nanfeng, empress and wife of Jin Huidi (b. 257)
- Liu Ling, Chinese scholar and poet (b. 221)
- Sima Yu, crown prince during the Jin Dynasty (b. 278)
- Sporus of Nicaea, astronomer and mathematician (approximate date)
- December 28 – Theonas, Patriarch of Alexandria
- Zhang Hua, official of the Jin Dynasty (b. 232)