In 86, the Dacian king Duras ordered his troops to attack the Roman province of Moesia on the southern course of the Danube river.
After this attack, the Roman emperor Domitian personally arrived in Moesia, reorganized the province into Moesia Inferior and Moesia Superior, and planned a future attack into Dacia.
Domitian, started a strong offensive against Dacia in 87, ordering General Cornelius Fuscus to attack. Therefore, in the summer of 87, Fuscus along with five or six legions crosses the Danube.
They encountered the Dacian army at Tapae, where the Romans were ambushed, suffering a great defeat. Almost all of the soldiers from Legio V Alaudae were killed, the Dacians captured their flags and war machines, and general Cornelius Fuscus himself was killed in battle.
After this victory, the Dacian king Diurpaneus received the name of Decebalus, meaning as strong (or brave) as ten men.
The Roman offensive continued the following year, with general Tettius Iulianus having now taking command. The Roman army entered Dacia following the same route Cornelius Fuscus did in the previous year. The battle took place mainly in the same area, at Tapae, this time the outcome being a Roman victory. Because of the difficult road to Sarmizegetusa, the capital of Dacia, and because of several defeats suffered by Domitian in Pannonia, the Roman offensive halted and Decebalus sued for peace.
Following the peace of 89, Decebalus becomes a client king of Rome, receiving money, craftsmen and war machines from the Roman Empire, to defend the empire's borders. Some historians believe this unfavorable peace for the Romans might have been the cause for Domitian's assassination in September 96.
Decebalus, the king of the Dacians, instead of using the money as Rome intended, decided to build new citadels in the mountains, in important strategic points, and to reinforce the existing ones.