The Ark of the Covenant was first introduced in the Bible as follows:
Exodus 25:8-22
“And let them make Me a sanctuary, that I may dwell among them. According to all that I show you, that is, the pattern of the tabernacle and the pattern of all its furnishings, just so you shall make it. And they shall make an ark of acacia wood; two and a half cubits shall be its length, a cubit and a half its width, and a cubit and a half its height. And you shall overlay it with pure gold, inside and out you shall overlay it, and shall make on it a moulding of gold all around. You shall cast four rings of gold for it, and put them in its four corners; two rings shall be on one side, and two rings on the other side. And you shall make poles of acacia wood, and overlay them with gold. You shall put the poles into the rings on the sides of the ark, that the ark may be carried by them. The poles shall be in the rings of the ark; they shall not be taken from it.
And you shall put into the ark the Testimony which I will give you. You shall make a mercy seat of pure gold; two and a half cubits shall be its length and a cubit and a half its width. And you shall make two cherubim of gold; of hammered work you shall make them at the two ends of the mercy seat. Make one cherub at one end, and the other cherub at the other end; you shall make the cherubim at the two ends of it of one piece with the mercy seat. And the cherubim shall stretch out their wings above, covering the mercy seat with their wings, and they shall face one another; the faces of the cherubim shall be toward the mercy seat.
You shall put the mercy seat on top of the ark, and in the ark you shall put the Testimony that I will give you. And there I will meet with you, and I will speak with you from above the mercy seat, from between the two cherubim which are on the ark of the Testimony, about everything which I will give you in commandment to the children of Israel”.
The Ark of the Covenant was permanently kept in the Holy of Holies, the most Holy Inner Sanctuary of the Temple.