| 285 | Diocletian and the Tetrarchy(285 to 305) | Diocletian split the Roman Empire into East and West. He added junior emperors, so there are four emperors, rather than just one, or even two. Civil war followed. |
| 306 | Christianity(306 to 337) | In 312, Constantine defeated his co-emperor at the battle of the Milvian Bridge. He became the sole ruler in the West, rather than one of two. Later Constantine defeated the Eastern ruler and becomes sole ruler of the Roman Empire. He established Christianity and founded the city of Constantinople. The Roman Empire did not remain united. |
| 378 | Battle of Adrianople (August 7, 378) | In August 378, Visigoths defeated the Eastern Roman Emperor, Valens. This is the first significant defeat of the Romans at the hands of the barbarians. |
| 379 | Theodosius Reunited Empire | Under the Emperor Theodosius, the Empire was briefly reunited; however, this did not continue after Theodosius' lifetime. |
| 395 | Death of Theodosius | Following his death, the Empire was again split, this time between his sons. |
| 401 | Visigothic Incursions(401 to 410) | Between 401 and 410, the Visigoths made progressive incursions further and further into Southern Italy. |
| 410 | Sack of Rome | Under the command of Alaric, the Visigoths sacked Rome for the first time in 410. This is sometimes listed as the fall of Rome; however, the city continued under the Western Emperor for some time after the sack of Rome by Alaric. |
| 420 | Barbarian Settlements(420s to 440s) | Between the 420s and the 440s, barbarian settlements of different sorts developed throughout the Roman Empire. These groups established autonomous and fully functional kingdoms. |
| 429 | Vandals Sacked North Africa(429 to 435) | Vandals, under the command of Gaiseric, sacked North Africa. North Africa was a key part of the Roman Empire, and was responsible for the majority of the grain supply. This action cut off the supply of grain to the city of Rome, as well as some other parts of the Empire. |
| 440 | Huns Began to Raid Eastern Empire(440 to 450) | The Huns, under the command of Attila the Hun, began to raid the Eastern Empire. While the fall of the Roman Empire most commonly refers to the Western Empire, the Eastern Empire was also in danger at this time. |
| 455 | Second Sack of Rome | In 455, Vandals, already in control of North Africa, again invaded and sacked the city of Rome. A relatively large number remained in the city, and they gained significant power. |
| 455 | Barbarian Generals(455 to 476) | After the sack of Rome, a number of Barbarian generals gained political and military power. |
| 476 | Deposition of Last Roman Emperor | The Barbarian general Odovacar deposed Orestes' son Romulus Augustulus, the last Roman Emperor. He notified the Eastern Emperor Zeno that there was no need for a new Western emperor. |
| 488 | Theodoric the Ostrogoth(488 to 493) | In 488, Theodoric the Ostrogoth was sent to the West by the Emperor in the East, Zeno. Theodoric unseated Odovacar and established an Ostrogothic kingdom in Rome. |
