Archaeologists have found a vast new network of royal tombs in Ethiopia, near the site where the 1,700-year-old Axum obelisk is to be re-erected.
The obelisks mark the graves of Axum's ancient rulers
Experts using sophisticated imaging equipment discovered the burial chambers, even older than the obelisk, under a 1963 car park, said the UN.
The stone monoliths were originally erected to mark burial sites for deceased members of the aristocracy.
The final piece of the Axum obelisk was flown home from Italy on Monday.
The whole structure - seen as a national religious treasure - is to be re-erected in September following the Ethiopian rainy season.
The obelisk was stolen by fascist Italian troops in 1937.
The archaeological team which discovered the new burial sites was sent to Axum to prepare for the re-erection of the obelisk.
Unesco director-general Koichiro Matsuura said it was likely that some of the tombs were still intact.
"The opening of these new tombs to the public would represent, moreover, an additional asset for the site, which, by boosting cultural tourism, would contribute to the economic development of the country," Mr Matsuura said.
A statement from the UN organisation said the site was a royal necropolis used by several dynasties before the Christian era. It added that the network stretched far beyond the perimeter of the present World Heritage Site.