Families who plan to bury an urn in a cemetery are often required to enclose and seal the urn into a separate urn vault. These urn vaults typically are made of polymer (high impact plastic) or sometimes concrete. The primary purpose of the urn vault is to protect the urn from the weight of the earth and any heavy cemetery maintenance equipment.
If a family has selected a brass urn, wood urn, or similar traditional urns, then the use of a separate urn vault is preferred. However, some families choose cultured marble and genuine marble urns as they can function without the separate component -- these urns hold the ashes inside and can be buried as is.