Final answer:
The correct answer is option a) The Gauls defeated the Roman army.
Step-by-step explanation:
The event you're asking about, the Sack of Rome by the Gauls, occurred in 387 BC (also often cited as 390 BCE). The historical context involves the peoples of Gaul, which included different Celtic tribes who occasionally engaged in conflict with Rome. The most notorious of these conflicts was the attack and subsequent sack of Rome by the Senones, a Gallic tribe, which led to the looting and burning of the city. Rome had previously been considered impregnable, and the sack shattered Roman confidence in their city's invincibility.
The Roman response was multifaceted over time. Led by figures such as Marcus Furius Camillus, they eventually drove the Gauls out and began a period of military reorganization, bolstering their defenses to ensure that such a disaster would not occur again. The Romans swore never to let Rome fall to an attack again, which led to changes in military tactics and the fortification of the city.
However, the Gallic Wars would continue, most famously under Julius Caesar who, about three centuries later, waged a relentless campaign against the various Gallic tribes. By this point in Roman history, Gaul had become deeply integrated into the empire as a wealthy province contributing significantly to the Roman elite and military power.