Final answer:
The Arno river is the waterway that flows through Florence and reaches the Ligurian Sea, having played an important role in the prosperity of Tuscan cities like Pisa.
Step-by-step explanation:
The river that flows through Florence and subsequently empties into the Ligurian Sea is called the Arno. This river passes through significant Italian cities, including Pisa, and extends to the Mediterranean Sea.
Historically, when the silt deposits had not yet pushed the coastline away, Pisa was an important port city due to its proximity to the sea. The Arno River has been essential in the development and prosperity of the Tuscany region, serving as a conduit for commerce and contributing to the area's rich maritime history.