I have been wondering about a spear being thrust into the ground, where it is more or less vertically standing up.. is this symbolic of anything? For some reason I am interpreting it as some kind of declaration of war, or as like a declaration of "this territory is mine" type thing.. is there anything to this?

I suppose I can mention what set me off on wondering about this.. in the movie Troy.. at the start Achilles is about to fight a one-on-one with the opposing army's champion.. and he has harsh words with the King he is in service to, and then thrusts his spear into the ground as he walks off to fight the duel.. now obviously I could just be desiring to read into this more, but it could simply be that he did not want to use the spear and so he just stabbed it into the ground until he came back to pick it up.

So yeah.. is there possibly any historic meaning or reference to spears being thrust into the ground and their meaning?