Final answer:
Livy's account of Aeneas's founding of Lavinium describes the foundation of the city of Lavinium.
Step-by-step explanation:
The important event described in Livy's account of Aeneas's founding of Lavinium is the foundation of the city of Lavinium. According to Livy, Aeneas, a Trojan hero, founded the city after fleeing the fall of Troy. Lavinium became an important city in ancient Rome and was considered one of the ancestral homes of the Roman people.