https://nabataea.net/explore/founding_of_islam/why-a-cube-q-a05/
"What are the origins of the Ka’ba? Why is it a cube? Where did the people get this idea from? Did it come from pre-Islamic history? Does it go back to Abraham? So several questions about the Ka’ba building.
First, for those of you who do not know much about Islam, the Ka’ba is a building. It is a cube shaped building, with a large black cloth over it, making it look like a large square black object. Worshipers circle around this cube shaped building. There are many people who think that the Ka’ba building is the black stone itself.
So, first of all, let’s put that idea to rest. The black stone is held in a silver container. It a small basalt type stone, possibly a meteorite. During the fighting over the stone, it was broken into seven pieces. These pieces are placed in a silver holder, which is attached to one corner of the Ka’ba building.
I call the Ka’ba a building, because that is what it is. The Ka’ba is made of stone blocks. Here is a photo of it, with the cover removed. It has a very large high door in one side, and inside there are a number of pillars. Here are some photos of the inside of the Ka’ba building. The Saudi Royal family is visiting the inside of the Ka’ba.
Al Ṭabarī tells us of a pagan Yemeni king, Al Tubba, around 400 AD, who marched north out of Yemen. (al-Ṭabarī starting about pg. 122 and again starting at pg. 166) He was upset with the Byzantines and was marching against them. First he conquered Yethrib, known as Medina today, leaving a son there to govern the area, and then he marched further north to Petra/Mecca. (Making Medina under Yemeni control) A group of men said to the king and his army: “Oh king, allow us to lead you to an ancient, largely obliterated treasury which previous monarchs have overlooked, which contains pearls, rubies, gold, and silver … It is in a place called Mecca here the people worship and pray. But two Jewish rabbis told the king that these men were planning his destruction. King Tubba asked why these Jews themselves did not worship at this temple.
The Jews replied: “It is indeed the temple of our forefather Abraham, and it is just as we have informed you; but the local people have placed obstacles between us and the temple. They have setup various idols around it, and they shed blood there. They are unclean polytheists.”