Final answer:
The Diptych of the Nicomachi and the Symmachi is significant for its depiction of mythological scenes, which highlighted the fourth-century Roman art's transition from strict classicism to a style embracing both realism and abstraction.
Step-by-step explanation:
The Diptych of the Nicomachi and the Symmachi is significant to the art tradition of fourth-century Rome for its depiction of mythological scenes. This ivory panel was commissioned to celebrate a marriage between two Roman patrician families, which showcases aesthetic practices of the period that sometimes broke away from classicism. It features stylistic elements, such as odd proportionality and spatial contradictions, esteemed by patrons of various religious backgrounds during that time, reflecting a blend of tastes and cultural influences in Roman art.
Roman art tradition during the fourth century exhibited a strong appreciation for the classical past but began to embrace more expressive qualities and less rigid naturalistic standards. This trend can also be seen in portraiture, such as the porphyry bust of Galerius, which depicted realistic facial features yet also leaned toward abstraction. The shift in style also encompassed a variety in subject matter, from imperial portraits to elaborate sarcophagi, and from mythological scenes to more symbolic and abstract presentations.