Experts say they have already unearthed the remains of 30 people, including 19 still intact as mummies, which are likely to be some of the oldest ever found in Peru.
The discovery is exceptional because some of the dead were religious sacrificial offerings and the site had not been plundered by grave robbers.
Archeologist Peter Eeckhout of Brussels Free University, who led the excavation project, said he had discovered "the remains of several cultures buried on top of each other".
It was not clear to which cultures the mummies belonged but they were likely to have been farmers and craftsmen who lived 500 years before the Inca empire was founded.
The graveyard is within the boundaries of the Pachacamac archeological complex 30km south of Lima and its discovery follows weeks of digs by archeologists.
In the latest discovery, four of the mummies probably died in ritual sacrifice and were either buried alive, killed by blows to the head or strangled, archeologists said.
Holding up the remains of a 2-year-old boy, British archeologist Lawrence Owens said: "The position of the body and the remains of his feces indicate he tried unsuccessfully to free himself from the burial bundle and was buried alive."
Another of those sacrificed was a 12-year-old boy whose skull was cracked at the front, probably by a heavy blow.
"We found a tumi knife close to the body and its size corresponds with that of the skull fracture," Owens said.
"If you ask me if this was a ritual sacrifice, I would say yes," he added. A mummified 35-year-old man with a rope around his neck was also among the four sacrificed.
Archeologists have uncovered thousands of mummies in recent years that mostly date from the Inca culture, including about 2000 unearthed from under a shantytown near the capital in 2002.