What does Deuteronomy 4:46 mean?

He gave them these laws while they were east of the Jordan, in the valley across from Beth Peor, in the land that used to belong to Sihon, king of the Amorites, who lived in Heshbon. Moses and the Israelites had defeated him when they came out of Egypt. Deuteronomy 4:46 - Modern Text Bible

(This sets the scene: Moses is speaking in territory Israel recently conquered, reminding them of God’s help.)