6 Build the altar of the LORD your God with fieldstones and offer burnt offerings on it to the LORD your God.

Read Deuteronomy 27:6 Using Other Translations

Thou shalt build the altar of the LORD thy God of whole stones: and thou shalt offer burnt offerings thereon unto the LORD thy God:
you shall build an altar to the LORD your God of uncut stones. And you shall offer burnt offerings on it to the LORD your God,
Build the altar of uncut stones, and use it to offer burnt offerings to the LORD your God.