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.
Emperor Diocletian issues his Edict on Maximum Prices, which, rather than halting rampant inflation and stabilizing the economy, over time adds to inflationary pressures by flooding the economy with new coinage and by setting price limits too low.
Great Persecution: Emperor Diocletian launches the last major persecution of Christians in the Empire. Hierocles is said to have been the instigator of 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.
Maximinus II (305–313) persecutes the Christians of Egypt, many of whom take refuge in the desert. In time, this refuge leads to the monastic life. In these monasteries Coptic writing develops, supporting the propagation of Christian texts.
Landowners dominate the Roman Empire and enjoy the title of senator, which exempts them from the crushing taxes imposed on the rest of the population. The Senate has lost all its power and the landowners almost never attend Senate sessions. Members of municipal senates (curiales or decuriones) are charged with the responsibility of collecting taxes and paying arrears; smaller landowners are held responsible for providing recruits for the Roman army and with keeping wastelands under cultivation.
In Yamato (Japan), the Kofun period dominated during this decade. It was an animistic culture which existed prior the introduction of Buddhism. A legend of the 4th century Prince Yamato Takeru alludes to the borders of the Yamato and battlegrounds in the area. A frontier was obviously somewhere close to the later Izumo province (the eastern part of today's Shimane prefecture). Another frontier, in Kyūshū, was apparently somewhere north of today's Kumamoto prefecture. The legend specifically states that there was an eastern land in Honshū "whose people disobeyed the imperial court", against whom Yamato Takeru was sent to fight. That rivalling country may have been located rather close to the Yamato nucleus area itself, or relatively far away. The today Kai province is mentioned as one of the locations where prince Yamato Takeru sojourned in his said military expedition.
Northern frontier of this age was also explained in Kojiki as the legend of Shido Shōgun's (四道将軍: Shōguns to four ways) expedition. Out of four shōguns, Ōbiko set northward to Koshi and his son Take Nunakawawake set to eastern states. The father moved east from northern Koshi while the son moved north on his way, and they finally met at Aizu (current western Fukushima). Although the legend itself is not likely to be a historical fact, Aizu is rather close to southern Tōhoku, where the north end of keyhole kofun culture as of late 4th century is located.