In the heated discussion about Sanxingdui, one of the most eye-catching archaeological discoveries of a civilization that flourished 3,000-5,000 years ago in southwest China's Sichuan Province, "alien" is among the top debated words. Why is that? Was Sanxingdui built by an alien civilization?

While this might unfortunately just be far-fetched thinking, let's look at some of the mysterious clues.