The Ark of the Covenant, which contains the Tablets, was constructed by Betzalel Ben Uri. It was placed inside the inner sanctum of the Temple in the Tabernacle, which was located in the Sinai Desert. The Ark had accompanied the children of Israel while they were wandering in the desert. It was placed in the Tabernacle in Shiloh and fell during the war with the Philistines. But after they were struck by a plague it was returned to the hands of the people of Israel, found in Kiryat Yearim, and was later brought up to Jerusalem by King David. It finally found its place in the Temple, which was built by King Solomon on Mount Moriah. The Ark was the holiest vessel, but towards the end of the period of the second Temple, it disappeared, and remained missing from the Holy of Holies throughout that time.
In the opinion of the Tanna, Rabbi Eliezer, the Ark was exiled to Babylonia during the destruction of the Temple. According to the opinion of other Tannaic sages, King Josiah
buried it inside tunnels under the Temple Mount in order to protect it from being exiled together with the Jewish people. In fact, towards the end of the construction of the Temple, King Solomon knew that it would be destroyed, so he built a deep, winding burial site in which to hide the Ark. This is where King Josiah eventually buried it.
Our sages recount that during the time of the second Temple, a Kohen noticed that there was one part of the floor of the wooden chamber that was different than the other parts. He came to tell his friend about his discovery, but before he had a chance to finish speaking, his soul had suddenly left him. From this they deduced that the Ark was in fact buried there.
As a result of this revelation, there are people today who believe that the Ark is still there, under the Foundation Stone, which is where it was previously located. One of those people was the Rabbi of the Western Wall, Rabbi Meir Yehuda Getz, of blessed memory. When they began excavating the Western Wall Tunnels, he made some calculations and instructed them to break into a certain area beneath the Temple Mount. They discovered a huge tunnel carved through a rock leading towards the east, under the Temple Mount. It measured 28 meters in length and 6 meters in width. The bottom of the tunnel was filled with water and mud.
In his journal, Rabbi Getz wrote: “I immediately ran to the site and was overwhelmed with excitement. I sat there for a long time sprawled helplessly as warm tears were streaming down my face.” According to his calculations, there was a certain place that led to the location of the Ark of the Covenant. But it didn’t take long for the Muslims to discover this opening. They broke in, and Rabbi Getz, together with his Yeshiva students tried to physically block the members of the Waqf from entering.
At the end of a stormy day, in which the Temple Mount was at the center of international attention, the Prime Minister of that time, Menachem Begin, ordered that the tunnel be closed. According to Getz's associates, he did in fact see the Ark in its place, but he covered the area and did not talk about it out of fear of being endangered by the Muslims.
When our sages say that the Ark was ‘concealed’, it probably means that it’s been concealed from our nation and its whereabouts will only be revealed to us in the days of the Third Temple.