And Moses stretched forth his hand toward heaven; and there wasa thick darkness in all the land of Egypt three days: 
They saw not one another, neither rose any from his place for three days: but all the children of Israel had light in their dwellings.
Exodus 10:22,23
"The 9th plague, of darkness, was an attack on the supreme 
deity of Egypt, the sun-god Ra or Amon-Ra (also spelt Re), who was 
believed to bring light and heat to the earth. 
Other sky gods also 
impotent were Horus, Seker, Khepri, Mut and Nut."
CMI 

