Alaric I
Service under Theodosius I

By 392, Alaric had entered Roman military service, which coincided with a reduction of hostilities between Goths and Romans. In 394, he led a Gothic force that helped Emperor Theodosius defeat the Frankish usurper Arbogast —fighting at the behest of Eugenius—at the Battle of Frigidus. Despite sacrificing around 10,000 of his men, who had been victims of Theodosius' callous tactical decision to overwhelm the enemies' front lines using Gothic foederati, Alaric received little recognition from the emperor. Alaric was among the few who survived the protracted and bloody affair. Many Romans considered it their "gain" and a victory that so many Goths had died during the Battle of Frigidus River. Alaric biographer Douglas Boin (2020) posited that seeing ten thousand of his (Alaric's) dead kinsmen likely elicited questions about what kind of ruler Theodosius actually had been and whether remaining in direct Roman service was best for men like him. Refused the reward he expected, which included a promotion to the position of magister militum and command of regular Roman units, Alaric mutinied and began to march against Constantinople.

On 17 January 395, Theodosius died of an illness, leaving his two young and incapable sons Arcadius and Honorius in Stilicho's guardianship. Modern writers regard Alaric as king of the Visigoths from 395. According to historian Peter Heather, it is not entirely clear in the sources if Alaric rose to prominence at the time the Goths revolted following Theodosius's death, or if he had already risen within his tribe as early as the war against Eugenius. Whatever the circumstances, Jordanes recorded that the new king persuaded his people to "seek a kingdom by their own exertions rather than serve others in idleness."
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