The reign of Emperor Trajan (AD 98-117) was the time of the greatest expansion of the Roman Empire. More than a century had passed since the Balkans came under the heel of Rome and the imperial administration assimilated the lands south of the Istros River (todays Danube). It was the preservation of the peace along the border rather than the need of new territorial gains that led to several military campaigns, which were a complete success for the Roman troops. The most significant of these was against the union of Dacian states under Decebalus. Dacians were tribes of Thracian ancestry, inhabiting the north part of the Danubian plain and the South Carpathians in modern Romania. The first Dacian War (AD 101-102) ended with partial Roman success and the signing of a peace treaty, which was humiliating for the Dacians. It was the reason for the start of the second Dacian War a few years later (AD 105-106), which resulted in the annihilation of the Dacian kingdom, the suicide of Decebalus in an attempt to avoid being taken prisoner by the Romans, and the annexation of the conquered territory as a new imperial province under the name of Dacia.