The Dacians, or Getae, had been left independent after Domitian’s Dacian Wars in the late 80s, their king, Decebalus, having received the status of "king client to Rome", receiving from Rome military instructors, craftsmen and even money.

Instead of using the money as Rome intended, Decebalus had elected to build new citadels in the mountains in important strategic points and to reinforce the existing ones.

Trajan, determined to stamp out the Getian menace, expand the glory of his reign, end a treaty perceived as humiliating, and take over the gold and silver mines of Transylvania, has decided to strengthen the dangerous Danube frontier by converting Dacia into a salient of Roman territory north of the river.

This would also dismember the Sarmatian tribes and remove the risk of large, hostile combinations to a safer distance.

Labeling Decebalus a menace to the security of Rome’s provinces to the south across the Danube, Trajan assumes personal command of a punitive expedition of the Dacian kingdom and, with a force of one hundred thousand men, launches his first campaign in 101.

The Romans lay down a road along the Danube and cross the river at Viminacium, slowly making their way into Dacia.