The Fermi Paradox springs to mind (where are they?) and since Fermi first posed it, our telescopes have greatly improved and we still see no 'astroengineering' efforts, The Planetary Society is (has?) sponsoring searches of considerable amounts of radio spectrum and has found nothing. No artifact on earth has ever been found of extraterrestrial origin (isotopic analysis could determine that) and there seems to be no credible evidence of recent close encounters of the third kind.
As for ancient contact reports, even for a civilization 'greatly' more advanced than us, it is anticipated that interstellar flight will remain difficult and/or lengthy. So, for 'someone' to have gone to the effort to visit earth, for example, 3000 years ago, it is curious they didn't stick around to see how things turned out, or more likely, that they didn't stick around and colonize earth.
As for ancient contact reports, even for a civilization 'greatly' more advanced than us, it is anticipated that interstellar flight will remain difficult and/or lengthy. So, for 'someone' to have gone to the effort to visit earth, for example, 3000 years ago, it is curious they didn't stick around to see how things turned out, or more likely, that they didn't stick around and colonize earth.
