He defeated the Chatti, annexed the district of the Taunus, and established the Limes as a line of defence; but he suffered defeats at the hands of the Quadi, Sarmatae and ' Marcomanni; in Dacia he received a severe check, and was obliged to purchase peace (90) from Decebalus by the payment of a large sum of money and by guaranteeing a yearly tribute - the first instance in Roman history.
A prince had arisen among the Dacians, Decebalus by name, worthy to be placed at the head of all the great barbarian antagonists of Rome.
He agreed to pay to Decebalus an annual subsidy, and to supply him with engineers and craftsmen skilled in all kinds of construction, but particularly in the erection of fortifications and defensive works.
In the following campaign, after desperate fighting to the north of the Danube in the mountainous region of Transylvania, Sarmizegethusa, the capital of Decebalus, was taken, and he was forced to terms. He agreed to raze all fortresses, to surrender all weapons, prisoners and !Roman deserters, and to become a dependent prince under the suzerainty of Rome.
In 105 began the new struggle, which on the side of Decebalus could now only lead to victory or to destruction.
85 to 89 the Dacians were engaged in two wars with the Romans, under Duras or Diurpaneus, and the great Decebalus, who ruled from 86-87 to 107.
Decebalus restored the arms he had taken and some of the prisoners and received the crown from Domitian's hands, an apparent acknowledgment of Roman suzerainty.
The result of his first campaign (101-102) was the occupation of the Dacian capital Sarmizegethusa (Varhely) and the surrounding country; of the second (105-107), the suicide of Decebalus, the conquest of the whole kingdom and its conversion into a Roman province.