Were demons afraid of the cross before the crucifixion? Afaik, the cross is a big christian symbol because of the crucifixion of Jesus (if it was before, wow the roman were dumb to nail a prophet to a sign of his own religion)

Also, Demons are usually repelled by holy symbols.

But were they afraid of the cross before the crucifixion, therefore before it became a christian symbol?

Scenario: we are in 200 BC and I encounter a demon. Would pulling out a cross still work as well as today?
The answer is yes.  The cross was foreshadowed as salvation and they trembled.  The first time was when Israel battled the Amalekites after coming out of Egypt roughly circa 2,000 BCE.  Joshua was sent to battle, while Moses was on the hill overlooking.


  And Moses said unto Joshua, Choose us out men, and go out, fight with Amalek: to morrow I will stand on the top of the hill with the rod of God in mine hand. And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed.
  Exodus 17:9, 11
  
  But Moses' hands were heavy; and they took a stone, and put it under him, and he sat thereon; and Aaron and Hur stayed up his hands, the one on the one side, and the other on the other side; and his hands were steady until the going down of the sun.  And Joshua discomfited Amalek and his people with the edge of the sword.
  Exodus 17:12-13


There's the sign of the cross.

God commanded Moses to build a memorial.  


  And Moses built an altar, and called the name of it Jehovahnissi:
  Exodus 17:15


Jehovahnissi means the LORD is my banner, my refuge.

PS. The word translated "rod" is not necessarily a "walking stick or cane", but may also be translated as tribe, as in Moses took his tribe of Aaron and Hur or as staff as in the wooden beam.