So was the star map really an invitation?

Well the only thing I could think of is that either the invitation is really a trap or it was a different group of Engineers that invited us.

Written by the guy behind LOST... I kid thee not, this might be the ONLY REASON there was such a fraudulent early premise inserted into this film. I mean, "Come on," did the ENGINEERS lose the map back to Earth or something? Didn't work.

Unless, but this still doesn't make sense, the ENGINEERS design each world such that should the lifeforms they invent get 'clever' enough to reach their BOMB SILO then they deserve to have a SPECIAL DELIVERY. But his is rubbish motivation ... no?

they like to pretend to be gods and create/seed life. they want to be worshiped. so they visited us several times, pointing to where they came from. 2000 years ago they saw we had evolved to much/to fast...being angry and afraid we would match or surpass them they were going to destroy us. something went wrong and only one survived, the one in the movie.

I don't know what it was any more. Come visit us at our top secret military base makes no sense

@kalypso And in 2 thousand years they never thought to try again?

Perhaps it was the engineers trying to teach us and help us to evolve saying this is where we come from? maybe they were testing Earth and we got too advanced and were on their way to wipe us out? or maybe they tested the Alien DNA on themselves - saw that they couldnt cope with it and were on their way to Earth to see if we were able to cope?- I guess this is a question ultimately for the writers though - maybe explained if a sequal is made?

as you said it was a top secret military base doing unethical things.. all died but one in cryosleep who woke up in the movie... there was only 5 or so pyramids... maybe the base was seen as failed and to dangerous to continue with and was stopped/abandoned/closed by the leaders of the "homeworld"..

RS suggested in interviews that the events of the prologue happened millions of years before any life had started on earth, and as most of the dead Engineers - especially the one on LV-426 - appear to be fossilised then surely we can assume they've been dead a very long time? I don't understand where people get 2,000 years ago from. I think the seeding of a planet with their own DNA is a form of Terra Forming. The star map is one of two things; a trace memory embedded in our DNA or, as some have suggested, a lure so the Engineers know that their work is done and the planet is ready to be repopulated. Either way, I believe they always planned to return to the planets they seeded and wipe out the indigenous population (they're genetic descendants). Unfortunately the weapon they created for this task got out of hand, mutated into the Xeno we all know and love, and destroyed them.