He was Marcus Ulpius Traianus (53 to 117 AD), a Roman soldier-emperor who conquered Dacia and campaigned against Parthia, expanding the empire to its greatest size.

What is Trajan famous for?

For his conquest of Dacia, commemorated on Trajan's Column, and for pushing the Roman Empire to its largest territorial extent (Dacia in the north and a brief reach to the Persian Gulf in the east), while Britain was already a Roman province.

What were the Dacian Wars?

Two campaigns (101 to 106 AD) in which Trajan conquered Dacia in modern Romania, defeated King Decebalus, and seized its gold, funding a vast building programme in Rome.

What is Trajan's Column?

A monument in Rome carved with a continuous spiral relief telling the story of the Dacian Wars; it is one of the best surviving depictions of the Roman army in action.

Why is Trajan called the best emperor?

The Senate honoured him as Optimus Princeps, 'the best ruler,' for his military success, public works and reputation for justice; later Romans held him up as the ideal emperor.

Did Rome keep Trajan's conquests?

Not all of them. His successor Hadrian abandoned most of the eastern gains as too costly to defend, though Dacia remained a Roman province for over 150 years.

Trajan: the emperor who made Rome largest

Under Trajan the Roman Empire reached its greatest territorial extent, adding Dacia and briefly reaching the Persian Gulf (Britain was already a Roman province). A professional soldier who rose to the purple, he conquered gold-rich Dacia, drove deep into the Parthian East, and won such a reputation for justice and energy that later Romans wished every new emperor might be "luckier than Augustus and better than Trajan."¹

A soldier on the throne

Marcus Ulpius Traianus was born in Spain² and made his name in the army before being adopted as Nerva's heir in 97 and becoming emperor in 98 AD³. Unlike many rulers he was a genuine field commander, sharing the march with his legions, and he set out to expand the empire rather than merely hold it.

Marble bust of Trajan with a wreath on his head and a sword strap across the chest — Marble bust of Trajan wearing the civic crown, a sword belt and the aegis. Glyptothek, Munich. Public domain

The Dacian Wars

In two hard campaigns (101 to 106 AD) Trajan conquered⁴ Dacia, in modern Romania, defeating King Decebalus and seizing his kingdom's famous gold.⁵ The victory paid for a building boom in Rome and was carved in spiralling detail on Trajan's Column, which still stands and remains our best picture of the Roman army at war.

Portrait of the emperor Trajan — The emperor Trajan. Public domain.

Under him Rome stretched from Britain to the Persian Gulf, its greatest size ever.

East to the Persian Gulf

Late in his reign Trajan turned east against the Parthian Empire, taking its capital Ctesiphon and reaching the Persian Gulf⁶, the farthest east Roman arms would ever march. But the new conquests were restless, revolts broke out, and Trajan fell ill and died in 117 AD on the journey home⁵.

Coloured 19th century map of Asia Minor, Armenia, Syria and Mesopotamia with the Parthian Empire — Map for Trajan's expedition against the Parthians, from Victor Duruy's History of Rome and of the Roman People (1883). Public domain

The best of emperors

His successor Hadrian judged the eastern gains too costly to hold⁷ and pulled the border back, but Trajan's reputation only grew. The Senate hailed him as Optimus Princeps, the best ruler, and he became the yardstick against which every later emperor was measured.

Gold Roman coin showing a horseman spearing a kneeling figure, with a Latin legend around the edge — Gold aureus of Trajan, struck in Rome about 105 to 107 AD, with the legend SPQR OPTIMO PRINCIPI and the emperor riding down a Dacian. BnF, Paris. Public domain

See how his soldiers fought in how the Roman legion worked, or meet the other great commanders of ancient Rome.

Sources and notes

Numbered notes in the text point to the works below.

Eutropius, Breviarium ab urbe condita, Book 8, 5: the Senate's acclamation for new emperors, 'felicior Augusto, melior Traiano'. ↩
World History Encyclopedia, “Trajan” ↩
Encyclopaedia Britannica, “Trajan” ↩
Julian Bennett, Trajan: Optimus Princeps. A Life and Times (Routledge, 1997). ↩
Cassius Dio, Roman History, Book 68: 14 (Decebalus' treasure found beneath the river Sargetia), 23 (the Senate grants the title Optimus), 28 to 29 (Ctesiphon taken; Trajan reaches the Ocean at the head of the Persian Gulf), 33 (death at Selinus in Cilicia). Loeb translation by E. Cary online at LacusCurtius: https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cassius_Dio/68*.html. ↩ a b
F. A. Lepper, Trajan's Parthian War (Oxford University Press, 1948). ↩
Livius.org (Jona Lendering), “Trajan” ↩
Wikipedia, “Trajan, Wikipedia”