“Then Joshua built on Mount Ebal an altar to Yahweh, the God of Israel, just as Moses the servant of Yahweh had commanded the Israelites. As it is written in the book of the Law of Moses, ‘an altar of un-hewn stones, on which no iron tool has been used.’ They offered on it burnt offerings to Yahweh. They sacrificed offerings of well-being.”
Mount Ebal was about twenty miles from Gilgal and Ai. Mount Ebal and Mount Gerizim were the two close mountains surrounding the valley as the mountains of cursing and blessing, about 40 miles north of Jerusalem. There they sacrificed for the first time with burnt offerings and offerings of well-being on a stone altar built to Mosaic specifications as in Deuteronomy, chapter 27. Notice that there is a specific mention of a ‘written book’ with the Law of Moses in it.