Mercy-Seat: Placed Upon the Ark of Testimony
Source: TTT
Exodus 25:21
Set the mercy seat atop the ark, and put the Testimony that I will give you into the ark.
Exodus 26:34
Put the mercy seat on the ark of the Testimony in the Most Holy Place.
Exodus 40:20
Moses took the Testimony and placed it in the ark, attaching the poles to the ark; and he set the mercy seat atop the ark.