They probably represented a rain god.
Stone heads with grim faces likely symbolized deities associated with war, protection, or death in various cultures. The seriousness and intensity of the expressions could convey power, authority, or a sense of awe to those who encountered them, possibly serving as guardians or focal points for religious rituals.
They likely represented the Rain God.
They didn't. They depicted people with human faces and forms. But many Egyptian gods had the heads of animals. When they were represented in art, they were shown with their god faces, which appeared like the heads of animals.
The most large ones are the Easter Island rock faces.
A stone head with a grim face is most usually associated with the Olmec.
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The civilization associated with a stone head with a grim face is the Olmec civilization. These stone heads, known as Olmec colossal heads, were created by the ancient Olmec people who lived in Mesoamerica between 1200 BCE and 400 BCE. The purpose and meaning of these sculptures are still not fully understood, but they are considered to be powerful and important representations of Olmec rulers or deities.
heads and tails
Those are the faces of Evil!
It is an idiom. It is referring to the large quantity of faces, not literally a sea of heads.
I'm gonna go with stone.
Stone monolithic sculptures.