Augustan History
The painting depicts a (probably invented) episode in the life of the Roman emperor Elagabalus, also known as Heliogabalus (204–222), taken from the Augustan History. Although the Latin refers to "violets and other flowers", Alma-Tadema depicts Elagabalus smothering his unsuspecting guests with rose petals released from a false ceiling. The original reference is this: