Watching the really weird ritual of the Oscars Red Carpet, I wondered why we walk on red carpets. Then I found this. It's a comprehensive history of red carpets.
The first mention of red carpets comes from the 5th century BCE, in Aeschylus's play, Agamemnon. "Clytaemnestra tries to convince Agamemnon to walk across the red carpet, insisting that he deserves special recognition for his accomplishments." So it's for special people!
In the modern era, it dates back to railroads. "The red carpet originated with the railroad. Conductors commonly rolled out the red carpet to direct passengers to the correct location on the train." So now important people know which way to go.
There you have it. Greek epics and railroads. By the way, Jessica Chastain looks amazing.