Final answer:
Increased trade and manufacturing changed the basis of Roman prosperity by fostering a market economy where regions specialized in specific goods. This led to high commercial and agricultural productivity and supported the Roman government and military.
Step-by-step explanation:
Increased trade leading to increased manufacturing significantly impacted the underlying basis of Roman prosperity. The specialization of goods and the development of a market economy allowed regions to focus on producing certain products based on local resources or skills, which were then transported to markets across great distances. The Roman Empire's manufacturing of higher-value goods primarily occurred on a small scale in workshops, yet these products still found their way around the Mediterranean through extensive trade networks, including seaports like Ostia. This economic system supported the functioning of the government and military through trade revenues and taxes, fostering a level of commercial and agricultural productivity that would not be seen again until many centuries later.