Cassius is the surname of a family from Asyria and Latium descended from Avidius Severus and Julia Cassius. Julia, a princess and descendant of royalty - last name was carried on by her only son, Avidius Cassius for Avidius feeling alienated from his father.
Feeling disconnected from his father, Avidius Cassius adopted the last name "Cassius" from his mother Julia Cassius. His wife, Volusia carries the name but for unknown reasons is mononymously known.
Cassius means "hollow".