The people complained about the lack of food and water during the Exodus, so God sent fiery serpents to bite them.

When many died from the bites, Moses asked God to take away the serpents. What did God tell Moses to do?

Make a brass serpent, put it on a pole, and tell the bite victims to look at it

And the LORD said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live.

And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived. Numbers 21:8