In the movie Prometheus, the back story and the purpose of the alien giants is never discussed. However, enough clues were provided for one to infer their agenda. As the movie progresses we find out that the outpost the scientists were exploring was built by the giants to work on a biological weapon. When the android was asked where the giants were headed before they had to suspend their take off, he responds, “Sometime to create, one must first destroy.” It becomes clear from the last 15 minutes of the movie that the giants were on a mission to destroy life on earth to give way to new life.
Myths about a race of giants that existed on earth are plenty. The ancient Greeks called them the Titans, in Mesopotamia the king Gilgamesh from The Epic Gilgamesh was powerful giant, the Inca and Maya believe that a race of giants existed prior to modern humans. The Maya however, being such diligent time keepers, tell us exactly when this race existed on earth.
In Prometheus, the pictographs the scientists discovered had pictures of giant people pointing to a constellation in the sky. The oldest of these was a cave painting from around 35,000 B.C. To the Maya, December 21, 2012 marks the end of a 5125 year cycle called a sun. According to the Maya the First Sun was inhabited by a race of giants and began on 23,614 B.C., well in the range of some of the evidence the scientists in the movie presented.
According to the android the giants were headed to earth to destroy its inhabitants with a bio weapon in order to create new life on the planet. Likewise for the Maya, the end of each sun was met with destruction that was necessary for life to blossom anew. In the movie, when the giant is about to rip the android’s head off, he caresses his face first then proceeds to dismember him. This kind gesture seems odd from an alien giant bent on world destruction. It seems that the giant cared for the android, but knew that his mission was more important. The Maya also realized the importance of the cycles. Being more in tune with nature, they anticipated these events and saw a divine mathematical order in them.
In the movie, the female scientists claims that the giants created modern humans and calls them engineers. This is an old idea made popular by Zecharia Sitchin in his books The Earth Chronicles, which he translated from cuneiform Sumerian tablets. In them he states that an alien race called the Anunnaki created humans in their image. He describes the Anunnaki as giant humans with super human powers.
In the opening scene of the movie we see an alien ship flying over the alien planet. One of the giants sees this and commits suicide by drinking a black substance that was later found inside the vases containing the bio-weapon. The ship flying overhead looked nothing like the space ship of the giants, and leads me to conclude that the giants were coming to the end of their cycle, and that the one standing by the waterfall understood this and decided to take his life.
The message in the movie is one of fear and/or understanding. For the scientists and crew, the fear of loosing life on earth overwhelmed their senses and drove their actions. For the Maya, the end of each sun was met with a profound understanding of the cyclical nature of time. They bravely stood by as faithful observers waiting for the day the cycle would end and life would rise anew.