The tombs discovered in Peru's Cotahuasi Valley are located on small hills surrounding the site.
The researchers have so far excavated seven tombs that contain at least 171 mummies from the site now called Tenahaha.
The mummies were found to be curled up, ie their knees were put up to the level of their shoulders and their arms were folded along their chest.
The corpses were bound with rope and wrapped in layers of textiles, 'Live Science' reported.
In a newly published book, archaeologist Justin Jennings, a curator at Toronto's Royal Ontario Museum, wrote, "The dead, likely numbering in the low thousands, towered over the living."
The mummified remains were in poor shape and showed signs of damage from water and rodents. Some of the mummies were intentionally broken apart, their bones scattered and moved between the tombs.
Carbon dating has placed the age of the site from 800 AD to 1000 AD. The excavations, carried out between 2004 and 2007, will provide clues about the lives of ancient Peruvians.