Koeppel studied at the University of Cologne and under the ancient art historian Heinz Kähler.
He joined the faculty of Classics at the University of North Carolina at Chapel Hill in 1969 and was professor emeritus at the time of his death.
[3] A series of studies of Roman state art appeared in the pages of the Bonner Jahrbücher beginning in 1969.
[4] He also co-authored a volume on Roman souvenirs and the material culture of ancient tourism.
[5] A photograph of him dressed as the Flamen Dialis was published in The World of Roman Costume.