The people of Israel traveled from Mount Hor along the way to the Red Sea. They wanted to go around Edom. But they grew tired on the way.
References for Numbers 21:4
So they spoke against God. They also spoke against Moses. They said to them, "Why have you brought us up out of Egypt? Do you want us to die here in the desert? We don't have any bread! We don't have any water! And we hate this awful food!"
Then the LORD sent poisonous snakes among the people of Israel. The snakes bit them. Many of the people died.
The others came to Moses. They said, "We sinned when we spoke against the LORD and against you. Pray that the LORD will take the snakes away from us." So Moses prayed for the people.
The LORD said to Moses, "Make a snake. Put it up on a pole. Then anyone who is bitten can look at it and remain alive."
So Moses made a bronze snake. He put it up on a pole. Then anyone who was bitten by a snake and looked at the bronze snake remained alive.