Columbaria (pl.) are specialized burial structures designed to house cinerary urns containing cremated remains. In ancient Etruscan and Roman practice columbaria, typically built wholly or partly underground, contained niches stacked vertically, each designed to hold a single urn. (The term derives from the Latin word columba, meaning dove, because the niches resembled dovecotes.) Compared to other types of burial sites, such as above-ground mausolea, columbaria offered an option that was relatively economical, allowing families to inter multiple generations in a single location. Columbaria are still used today, often located in cemeteries and crematoria, or adjacent to churches and Buddhist temples. Web resource here and here.

Columbarium in the Tomb of the Scipios, Rome. Roman Republic. Early 3rd c. BCE–early 1st c. CE.