The recorded history of Westeros stretches back over 12,000 years in Martin's world, and long before humans inhabited the content it was home to a race of creatures known as the Children of the Forest. These non-human creatures were small, had brownish skin, and eyes much like cat eyes. They also possessed strong magic.
The Children of the Forest worshiped the old gods and were the beings that carved the faces into the weriwood trees throughout the continent. These are the same gods that the Starks and other northerners worship, unlike the new gods (the Seven) that southerns prayed to.