“Joshua summoned the twelve men he had appointed from the Israelites, one per tribe. Joshua told them, “Go in front of the ark of the LORD your God to the middle of the Jordan. Each of you is to put a stone on his shoulder, according to the number of the Israelite tribes. The stones will be a reminder to you. When your children ask someday, ‘Why are these stones important to you?’ tell them how the water of the Jordan stopped flowing before the ark of the covenant of the LORD. When it crossed the Jordan, the water of the Jordan stopped flowing. These stones will be a lasting memorial for the Israelites.””
Joshua 4:4-7 NET
https://www.bible.com/107/jos.4.4-7.net