Humans have been burying their dead for thousands of years. In fact, according to the fossil record, Neanderthals were the first humanoids to bury their dead over 300,000 years ago (Tappen). The first known burial site in existence was 300,000 years ago at the site of Atepuerca, Spain. At this burial site, over 32 individuals were found in a pit cave. In later years, around 100,000 years ago, there was evidence of bones being stained with red ochre (Thames). This leads archaeologists to believe that even back then there was something ritualistic and spiritual about burying the dead.
Tappen, N.C. 1985. The Dentition of the “Old Man” of La Chapelle-aux-Saints and Inferences Concerning Neanderthal Behavior. American Journal of Physical Anthropology 67(1):43-50.