Exodus 40:20

He took the Testimony and placed it in the ark, attached the poles to the ark and put the atonement cover over it.

(New International Version)

Then he took the testimony and put it into the ark, and attached the poles to the ark, and put the mercy seat on top of the ark.

(New American Standard Bible)

And he took and put the testimony into the ark, and set the staves on the ark, and put the mercy seat above upon the ark:

(King James Version)