Final answer:
Mid Republican Architectural decor was a mixture of A) simplicity in construction, with public buildings using vivid paints and structural decorations, and grandiosity in portrayal, as seen in high relief panels displaying military conquests.
Step-by-step explanation:
The Mid Republican Architectural decor in ancient Rome was characterized by a mix of simplicity and grandeur, reflecting various influences across periods. The Third Style of wall painting, considered a part of the Mid Republican era, was notable for its fantastical and stylized elements that departed from realistic architectural representations.
It featured ornamentation such as columns and pediments that were more artistic than structural, as well as small vignettes and bucolic scenes.
Additionally, public structures like temples and palaces during the period were adorned with vivid paints, gold leaf, and enameled terra cotta panels that provided both decoration and structural support. Roman architects in this era started to experiment with concrete, enabling them to construct grander scale buildings.
There was also a trend toward illustrating military conquests in high relief panels on structures such as the Arch of Marcus Aurelius, suggesting that while some aspects were simplistic, other elements of Mid Republican decor were quite elaborate.