Ark of the Covenant: Covered with the Vail by the Priests Before Removal
Source: TTT
Numbers 4:5, 6
Whenever the camp sets out, Aaron and his sons are to go in, take down the veil of the curtain, and cover the ark of the Testimony with it. / They are to place over this a covering of fine leather, spread a solid blue cloth over it, and insert its poles.