An oblong piece of solid gold, 212 by 112 cubits (about 30 by 18 inches), which was placed over the Ark of the Covenant (Exodus 25:37).
At both ends were two cherubim of beaten gold facing each other, and their faces bent downward towards the propitiatory; their wings overshadowed the oracle.
The propitiatory was the most sacred object of the Hebrew worship; it was looked upon as the throne of Jehovah who, from above the propitiatory, from between the cherubim, spoke to Moses and issued His commands to the children of Israel.
Before the exile, when the high priest entered the holy of holies on the Day of Atonement, he sprinkled with his finger towards the oracle the blood of the bullock and of the he-goat offered in sacrifice on that day (Leviticus 16).
New Catholic Dictionary