Kenneth Bulmer 
Cycle of Nemesis 

Seven thousand years ago one of Earth’s earliest civilisations was confronted by a menace from the stars — and died in a world-shaking effort to destroy that cosmic monster. But the death of that forgotten empire was not in vain, for they did succeed in entombing that dimension-shaking thing out of sight and harm to humanity. But even their efforts could not make that burial permanent — and after seven millennia the monster stirred again, cracking through the new world of today.