And there shall you build an altar unto the LORD your God, an altar of stones: you shall not lift up any iron tool upon them.
All Commentaries on Deuteronomy 27:5 Go To Deuteronomy 27
Gregory the Theologian
AD 390
It was once counted a glory for the altar that no axe had been lifted upon it, no stonecutter’s tool seen or heard. The higher meaning was that whatever was consecrated to God should be natural and free from artifice.