The Cobra is one of the oldest sacred symbols in Ancient Egypt. It was a symbol of The Lower Kingdom Of Ancient Egypt, and was depicted on the red crown of the north.
The Cobra was the symbol of royalty and a state emblem after it merged with the symbol of The Upper Kingdom in south, which symbol was The Female Vulture ( Nekhbet )
The Cobra (Wajet) was the most prominent symbol on The Crowns Of The Kings Of Ancient Egypt throughout its various eras.
Wajet was a symbol of protection for agricultural lands and houses surrounding them, as The Cobra is the strongest living creature in agricultural lands.
For This Reason, Wajet was the symbol of The Lower Kingdom from the beginning, as The Lower Kingdom was agricultural in most of its parts.
The Cobra ( Wajet ) was and still is a symbol of protection, strength, and divine care, in addition to being a symbol of Egyptian Royalty.

