How did Vespasian become emperor in 69 CE?

In the chaotic "year of the four emperors" (69 CE), Vespasian rose to power through military support rather than traditional senatorial appointment. Following the death of Nero and the subsequent instability, the Roman legions stationed in the East and along the Danube declared their allegiance to Vespasian, who was then serving as a commander in Judaea.12

As documented in the Historiae by the Roman historian Tacitus, this period was marked by intense civil war. After the suicide of the emperor Otho, the Senate initially recognized Vitellius; however, Vespasian’s forces—specifically the Danubian legions—defeated the Rhineland troops supporting Vitellius in a second battle near Cremona.312

Following the death of Vitellius, the Senate formally pronounced Vespasian emperor on December 21, 69 CE. Vespasian, however, remained transparent about the military origins of his rule, dating his authority to July 1, the day his troops first acclaimed him. This transition established the Flavian dynasty, which Tacitus later characterized as a period where the emperor was the only one to have "changed for the better".245