Final answer:
The Romans built their fleet through strategic military and economic policies, control over trade, and innovative engineering, which included the use of concrete and the construction of extensive road and sea networks.
Step-by-step explanation:
The process by which the Romans were able to build their fleet involved a combination of strategic policies and innovative engineering.
The Roman Senate implemented tactics such as divide and conquer, negotiating from strength, and establishing colonies as defense outposts, linked by well-constructed roads.
Roman military and economic strategies, such as transforming former enemies into allies, controlling trade via the class of shipowners known as navicularii, and engineering prowess in road and bridge building, also played significant roles.
The construction of seaports such as Ostia and leveraging sea routes for cheaper transportation were crucial. Moreover, the use of concrete allowed the Romans to build infrastructure like theaters and amphitheaters wherever they desired, supporting both social and military needs. These factors collectively enabled the Romans to build a formidable fleet and maintain command over the Mediterranean region.