What structure type in ancient Rome served as a multi-family apartment building?

The multi-family apartment building in ancient Rome is known as an insula. This architectural form was essential in accommodating the growing urban population, especially in cities like Rome where space was limited. Insulae were typically constructed with several stories, with the lower levels often being more desirable and, consequently, more expensive. These buildings provided living spaces for the lower and middle classes, featuring multiple units within a single structure.

In contrast, a basilica served primarily as a public building for legal and civic proceedings rather than as residential space. A domus refers specifically to a single-family home that was often the residence of wealthier citizens, whereas an amphitheater was designed for public spectacles such as gladiatorial games or theatrical performances. The insula thus stands out as the correct choice because it fulfilled the specific function of providing multi-family accommodation in the urban landscape of ancient Rome.