Syrian origin of the name Cassiodorus was demonstrated by A. J. Letronne.[] He identified the connection with the cult of Zeus Cassius, centered on Mount Cassius between Antioch and the sea, across the Orontes from Seleucia.[] Fridh asserts that the cult continued at Seleucia and near Pelusium even into the sixth century.[] It was attended by the apostate Julian while he resided at Antioch.[] The name itself appears in Greek inscriptions three times (twice in the genitive, Kasiodorou once in the nominative, Kassiodoros);[] these inscrip- tions are the best evidence for the accepted spelling of the name ending in -rus. Scholars before Mommsen's edition of the Variae usually accepted Cassiodorius, for the oldest manuscript of any of Cassiodorus' works dates from the late sixth century and gives the genitive very clearly as Cassiodorii.[] But that testimony is apparently only secondhand. M.J. Cappuyns had an ingenious solution to accommodate all the evidence, arguing that the name was Cassiodorus through three and a half generations known to us (MSS of the Variae are unanimous in using -rus), but that in his pedantic old age Cassiodorus Senator added the iota for etymological elegance.[] This is a quaint thesis but altogether unlikely.
It should finally be noted that Cassiodorus' known relative at Constantinople, Heliodorus, bears a name ending in a similar -dorus.