Final answer:
Trajan Decius's portraiture marked a shift in the stylistic approach by showing the emperor's anxiety and concern, signifying cultural and political shifts within the empire. Later portraits, like that of Galerius, moved towards abstraction, setting the precedent for medieval Christian art styles. Portrait evolution, such as that of Marcus Aurelius, mirrored changes in the emperor's life and the empire's condition.
Step-by-step explanation:
In portraying the personality of the emperor, particularly his sense of concern about the weakened state of the empire, the portraits of Trajan Decius began a new trend in portraiture. The approach to imperial portraits transitioned during his reign, moving from the idealized and stylized forms of previous emperors to a more expressive representation that conveyed the emperor's anxiety and concern.
Official portraits of emperors played an essential role in communicating with subjects, often portraying them as generals, magistrates, priests, or divine figures. The late antique style, as seen in the portraits of figures like Galerius, began introducing more abstract and expressive qualities, prefiguring the styles of medieval Christian iconography.
Likewise, the portrait types of Marcus Aurelius evolved over time, reflecting the emperor's maturation and eventually his age. The shift in style was not only a reflection of individual personality but also indicative of the broader cultural and political changes happening in the empire.