How did the Roman conquest of Dacia strengthen the Danube frontier?

The Roman conquest of Dacia under the emperor Trajan significantly strengthened the Danube frontier by eliminating a major regional power that had frequently threatened Roman security in the Balkans.12

By defeating the Dacian state, which had been unified under Decebalus and posed a persistent military challenge to the province of Moesia, Rome removed a source of instability along its northern border. The annexation of Dacia created a new defensive zone north of the Danube, within the curve of the Carpathian Mountains. This strategic buffer was designed to absorb and mitigate the movements of nomadic groups migrating from the steppes of southern Russia, thereby providing greater protection to the Roman territories situated south of the river.3124