Ancient writers - including Plato - linked it with human sacrifice to Zeus, a practice which has very rarely been confirmed by archaeologists anywhere in the Greek world and never on mainland Greece.
HUMAN SACRIFICE
According to legend, a boy was sacrificed with the animals and all the meat was cooked and eaten together.
"Several ancient literary sources mention rumours that human sacrifice took place at the altar, but up until a few weeks ago there has been no trace whatsoever of human bones discovered at the site," said excavator David Gilman Romano, professor of Greek archeology at the University of Arizona.
The central altar and a platform carved out of the mountain's rock were excavated in recent months. It's here the human skeleton was found.
"Whether it's a sacrifice or not, this is a sacrificial altar... so it's not a place where you would bury an individual. It's not a cemetery," Romano told The Associated Press.
A very unusual detail, he said, was that the upper part of the skull was missing, while the body was laid among two lines of stones on an east-west axis, with stone slabs covering the pelvis.
Some of the stone panels were richly carved.
So far, only about seven per cent of the altar has been excavated, between 2007-2010 and again this year.
"We have a number of years of future excavation to go," Romano said. "We don't know if we are going to find more human burials or not."
LINKED TO LEGEND
According to one of several versions of the Greek legend, King Lykaon was widely feared for his cruelty. He also seems to have been something of a sceptic, doubting the powers of the king of the gods - Zeus.
So he sacrificed to the god the roasted flesh of his son Nyctimus, served among the meat of a multitude of animals. The idea was to see if Zeus was omniscient enough to notice.
The god did.
Enraged, Zeus threw over the altar, turned King Lykaon into a wolf and killed all those involved in the murder with lightening.
HOLY PLACE
The mountaintop in the Peloponnese region is the earliest known site where Zeus was worshipped, and even without the possible human sacrifice element it was a place of massive slaughter. From at least the 16th century BC until just after the time of Alexander the Great, tens of thousands of animals were killed there in the god's honour.
Human presence at the site goes back more than 5000 years.
There's no sign yet that the cult is as old as that, but it's unclear why people should otherwise choose to settle on the barren, exposed summit.
Zeus was a sky and weather god who later became the leader of the classical Greek pantheon.
Pottery found with the human remains dates them to the 11th century BC, right at the end of the Mycenaean era, whose heroes were immortalised in Greek myth and Homer's epics, and several of whose palaces have been excavated.
Excavations at Mount Lykaion have uncovered monumental buildings in a sanctuary on a lower plateau. It was a site of ancient games held in honour of Zeus in the 4th Century BC.
The altar itself is much higher up the mountain. Most of the animal sacrifice remains there were of goats and sheep.
Archaeologists have found evidence the site had been occupied since Neolithic times.