480 BC – Battle of Veii (480 BC) – Consuls Marcus Fabius Vibulanus and Gnaeus Manlius Cincinnatus win a heavy battle against Veians and their Etruscan allies. Gnaeus Manlius Cincinnatus and former consul Quintus Fabius are slain.
46 BC, 6 February – Battle of Thapsus – Caesar defeats the Pompeian army of Metellus Scipio in North Africa.
45 BC, 17 March – Battle of Munda – In his last victory, Caesar defeats the Pompeian forces of Titus Labienus and Gnaeus Pompey the Younger in Hispania. Labienus is killed in the battle and the Younger Pompey captured and executed.
43 BC, 14 April – Battle of Forum Gallorum – Antony, besieging Caesar's assassin Decimus Brutus in Mutina, defeats the forces of the consul Pansa, who is killed, but is then immediately defeated by the army of the other consul, Hirtius
43 BC, 21 April – Battle of Mutina – Antony is again defeated in battle by Hirtius, who is killed. Although Antony fails to capture Mutina, Decimus Brutus is murdered shortly thereafter.
The Roman Empire under the Tetrarchy, with the territory of Constantius (yellow), Maximian (green), Galerius (pink), and Diocletian (purple)
The Roman Empire in 337, showing the Empire under Constantine (shaded purple) and other Roman dependencies (light purple).
The 4th century begins with civil war resulting in the ascendancy of Constantine I, then, after his death, the progressive Christianization of the empire, and wars with Sassanid Persia and Germanic tribes, punctuated frequently with more civil wars.
363, 29 May – Battle of Ctesiphon – Emperor Julian defeats Shapur II of Persia outside the walls of the Persian capital, but is unable to take the city.
363, June – Battle of Samarra (363) – Julian fights the Sassanids and is subsequently killed in battle. Though indecisive, the battle leads to massive losses for the Roman Empire through a forced peace treaty.
Roman–Sasanian War of 421–422 - The Eastern Roman Emperor Theodosius II declared war against the Persians and obtained some victories, but in the end, the two powers agreed to sign a peace on the status quo ante.
By 650 (pictured) the Eastern Roman (Byzantine) empire had lost all its southern provinces, except the Exarchate of Africa, to the Rashidun Caliphate. At the same time the Slavs invaded and settled in the Balkans. The losses continued in the next century
The Eastern Roman empire adopted the Greek language as official language under emperor Heraclius in 610. The Eastern empire shrunk to Greece and Anatolia, because of Persian, Avar and finally Arab invasions.