300

The year 300 was a leap year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Valerius. The denomination 300 for this year has been used since the early Middle Ages / Medieval period, when the Latin language term / abbreviation "Anno Domini" for the calendar era became the prevalent universal / worldwide method for naming and numbering years. First beginning in Europe at the end of the Roman Empire in the early Middle Ages / Medieval period.
Then the Christian-oriented dating system then spreading west across the Atlantic Ocean with the Western European explorers and religious faith to the continents of the Americas of the Western Hemisphere, then through the simultaneous movement of the various Christian churches, and Europeans along sea trading routes with the military / political / economic / social influences of Colonialism / Imperialism spread worldwide to Africa, Asia and Australia / Oceania.

Events

Emperor Diocletian begins construction of a palace that will become the city of Split. Diocletian, who plans on abdicating, intends to use this palace as his place of retirement.
Caesar Constantius I wins a victory over the Franks.
Asia
The lion becomes extinct from Armenia.
The Yayoi period ends in Ancient Japan.
Wootz steel is developed in India.
The Kama Sutra, an Indian handbook on the art of sexual love, is probably produced around this time by the sage Vatsyayana.
Micheon becomes ruler of the Korean kingdom of Goguryeo.
Africa
The elephant becomes extinct in North Africa.
The Atlas wild ass becomes extinct.
Mesoamerica
The Formative/Preclassic period in Mesoamerica comes to an end approximately 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.
By topic

The magnetic compass for navigation is invented in China.
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.
Diocletian's Palace, Split, Croatia, is built. Its model is nowadays kept at the Museo della Civilta Romana, Rome.
Religion
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.
Approximate date of the Synod of Elvira in Elvira, Spain, which prohibits interaction with Jews, pagans, and heretics.