Archaeologists working in northern Peru have discovered a spectacular tomb complex about 1,000 years old.
The discover of tumis in situ is particularly exciting to scientists
The complex contains at least 20 tombs, and dates from the pre-Inca Sican era.
Among the discoveries are 12 "tumis", ceremonial knives which scientists have not been able to study in a burial site before, as well as ceramics and masks.
The Sican culture flourished from approximately AD 800-1300, one of several metalworking societies which succumbed to drought and conquest.
Archaeologists working on the project say the find will help them understand details of the culture.
"It is a religious city, a sacred settlement, and at each excavation site is a cemetery," Izumi Shimada told Peru's El Comercio newspaper.
"That tells us that Sican was a very organised society."
Professor Shimada, based at the University of Southern Illinois in the US, has been excavating Sican sites for a quarter of a century. The latest dig was performed in conjunction with the Sican National Museum.
The burial site sits on Peru's northern coast, near the town of Ferrenafe.
Discoveries in the tomb complex include tumis formed from an alloy of silver, copper and gold; masks, breastplates and ceramics.
Buried in a pyramid 30m (100ft) long, archaeologists found the bones of a woman in her early 20s surrounded by figurines of Sican gods, ceramics and objects in copper and gold.
The site contains at least 20 tombs, making it a "religious city"
Another set of bones, clearly from a person of some stature, were found in a seated position accompanied by a metallic crown, part of a thorny oyster, and various ceramic objects including a vase.
The tumis are a prize find, because until now the knives have come to scientists from tomb raiders. Finding them in situ would allow a closer understanding of their role in Sican culture, researchers said.
One of the tumis features a representation of Naylamp, the mythical founder of Sican society who according to legend emerged from the sea and became a god.
The Sican were noted for producing gold, silver and copper in quantities which were substantial for the period.
They traded shells and stones with societies in what are now Ecuador, Chile and Colombia.
Their civilisation had already declined by the time that the mightiest of Peruvian cultures, the Inca, rose to prominence about AD 1200.