Loculus (architecture)

Loculus (Latin, "little place"), plural loculi, is an architectural compartment or niche that houses a body, as in a catacomb, hypogeum, mausoleum or other place of entombment. In classical antiquity, the mouth of the loculus might be closed with a slab, plain, as in the Catacombs of Rome, or sculptural, as in family tombs at Palmyra.

...
Wikipedia