"It was an immense slaughter, greater than had ever occurred in any former naval action. Thus the river was filled with dead bodies."
- Historia Nova, Zosimus
As winter fell in AD 386, the Eastern Roman Empire found itself in a position of delicately-balanced stability.
The Gothic War had ended four years prior, thanks to a peace deal that granted the Goths Roman lands in the northern parts of the Diocese of Thracia on which to settle and farm. In return for this, their fighting men were to muster for imperial military service if and when Emperor Theodosius called upon them. This system of gradual cultural integration and laying aside of old grievances was only just beginning to settle into place.
So, the last thing Emperor Theodosius needed was for a huge host of erstwhile unknown Goths to descend from the north and appear at the River Danube, demanding entry into the empire.
Full article (free, no paywall or anything) here:
https://www.gordondoherty.co.uk/writeblog/the-horde-of-odotheus