Deuteronomy 27:5
Then you must build an altar there to the Lord your God, an altar of stones -- do not use an iron tool on them.
Exodus 20:25
If you make me an altar of stone, you must not build it of stones shaped with tools, for if you use your tool on it you have defiled it.
Exodus 24:4
and Moses wrote down all the words of the Lord. Early in the morning he built an altar at the foot of the mountain and arranged twelve standing stones -- according to the twelve tribes of Israel.
Joshua 8:30-31
Then Joshua built an altar for the Lord God of Israel on Mount Ebal,
1 Kings 18:31-32
Then Elijah took twelve stones, corresponding to the number of tribes that descended from Jacob, to whom the Lord had said, "Israel will be your new name."