The first confirmed burials in ancient Sumeria happened around 5000 BC. They believed in an after-life, described as a land beneath earth (aka land of the living).
Usually, they buried their deceased in constructions in the ground next to their home (you remember after-life: near to earth), so the grave could be often visited and food was brought to it, news were told, and so on. Cremation was unusal, because the Sumers believed if a body was burned its human soul would go towards to the realm of gods where this soul could not find a home to stay.

If family members were not buried regulary, they could return as ghosts to haunt the living: a ghost entered the world of the living and causes problems at their homes, or, in more serious cases, as possession in which the ghost entered into the individual through the ear and tried to destroy one’s personal life and health.