- last post: 01.01.0001 12:00 AM PDT
i think that there are still a sizable amount of elites that are part of the prophets fleet who do not have any idea of the betrayal that happened and are still loyal to the prophet. if you think about it, at the end of halo 2 the prophet warped to earth and the battle had already been going on. i believe that the prophet sent the large fleet to earth to begin the battle, went to high charity to eliminate the remaining elites (which he believed to include the arbiter and half jaw) and gave the index to tartaurus to start the great journey.
its also possible that he does not believe in the great journey and only gave the index to taurtarus because he knew the blast would eliminate the flood that were going to invade high charity. this would mean that the ark has a completely different purpose that we do not know of.
also to set things straight on the gravemind. he is an all knowing entity, possibly as old as time. he can control computer systems (evidenced by his ability to use halo's teleport grid, assimilate the moniters, talk to cortana etc) this is supported by the fact that on the level gravemind (i believe) the area that cortana says has the most robust A.I resitance is the area that is dominated by the graveminds tentacles hanging down from the roof (you can see them in the area with the large broken window)
the gravemind reached high charity because he can travel as parasites do (flood are parasites) he probably created a spore of himself and travelled on the human ships to high charity before creating his new self inside of high charity. He most likely invaded high charity because of its slipspace capability.