Beneath the Gates: Fantasy, Archaeology, Science Fiction

Who created the mysterious arches, referred to on nearly every planet on the far side of galaxy as the "Gates of Life?" Archaeologists and xenobiologists of every ilk seek funding to uncover the baffling origin of these towering gates' existence.
One culture retains the practice of carrying newborns beneath the Gates. Others tore them down. On a few worlds, the Gates are feared or worshipped. The consistency of the ruins points to a single use and advanced creators. But who built them, and w...