Domitian's Dacian War

Domitian's Dacian War was a conflict between the Roman Empire and the Dacian Kingdom, which had invaded the province of Moesia. The war occurred during the reign of the Roman emperor Domitian, in the years 86–88 AD.

The Dacian attack in 86 and the defeat of Oppius Sabinus
At the end of 85 or the beginning of 86 AD, the Dacian king Duras ordered his troops to attack the Roman province of Moesia on the southern course of the Danube river. The Dacian army was led by Diurpaneus, the later king Decebalus. It seems that Romans were caught by surprise, since the governor Oppius Sabinus and a legion, probably the V Alaudae, were annihilated.

Following this attack, the Roman emperor Domitian, accompanied by Cornelius Fuscus, Prefect of the Praetorian Guard, personally arrived in Moesia, reorganized the province into Moesia Inferior and Moesia Superior, and planned a future attack into Dacia. To replace the lost legion and greatly strengthen the Roman army at this section, the IIII Flavia from Dalmatia and two more legions, the I and II Adiutrix, from western provinces were moved to Moesia. The region of Sirmium was attached to Moesia Superior, in order to have a single command over the endangered Dacian frontier.

Historians are divided as to what happened next. A. Mócsy suggests that after handing over the command to Fuscus, Domitian returned to Rome in the same year, while Fuscus cleared the Dacian invaders from the province. According to E. T. Salmon and M. Bunson, however, Domitian personally led the successful operations then he returned to Rome to celebrate a double triumph.

The defeat of Cornelius Fuscus
In the same year (86), after the initial success against Dacians, Cornelius Fuscus crossed the Danube. However, his army was ambushed and destroyed while Fuscus himself died in the battle. According to E.T. Salmon and other historians, this was the battle where Legio V Alaudae was annihilated. At any case, this legion subsequently disappeared from the Roman army list.

After this victory, Diurpaneus received the name of Decebalus, meaning as strong as ten wild men.

The battle of Tapae
The Roman offensive continued the following year, with general Tettius Iulianus now in command. The Roman army entered Dacia, advancing from Viminacium towards the Iron Gate Pass. The battle took place at Tapae, in 88 AD, but this time the outcome was a Roman victory.

Peace
After the battle, the course of events is unclear and a satisfactory chronological reconstruction is not possible. Suetonius mentions that there were "several battles of varying success" (against the Dacians). Lucius Antonius Saturninus, commander of the Roman army in Germania Superior, revolted. In addition, Iazyges, Marcomanni and Quadi refused to provide troops to Domitian for his Dacian war. Domitian killed their peace emissaries and attacked them, then he left for Rhine. He was forced to return to Pannonia after the Romans had suffered a defeat there. All these problems halted the Roman offensive and Decebalus, now the Dacian king, sued for peace, sending his brother, Diegis, as his plenary representative. Under the terms of the treaty, Decebalus returned the Roman prisoners of war but he was also lent a number of Roman engineers who helped him in building defensive fortifications. The Romans would pay an annual subsidy of 8 million sesterces and Decebalus was recognized as a client king of Rome.

Aftermath
For the remainder of Domitian's reign Dacia remained a relatively peaceful client kingdom, but Decebalus used the Roman money to fortify his defences. Domitian probably wanted a new war against Dacians, and reinforced Upper Moesia with two more cavalry units brought from Syria and with at least five cohorts brought from Pannonia. Trajan continued Domitian's policy and added two more units to the auxiliary forces of Upper Moesia, and then he used the build up of troops for his Dacian wars.