Why the smaller stones just above the huge stone?
The fury poured out upon the Temple by the Romans resulted in the destruction of most structures associated with the Temple Mount. Miraculously, the Western Wall, by and large, remained intact - damaged - but intact. Chisel marks found along the top of this stone are mute evidence of the Roman demolition efforts. They came this far - and then they gave up. Their attempts to topple the wall were unsuccessful. This is history. We're standing right where it happened.
When the Arabs built their mosque on the Temple Mount, they found the Western Wall in its damaged condition. Their building projects included restoring the walls of the Temple Mount. The huge stones from the top of the Western Wall were lying literally at their feet, exactly where they had fallen so many centuries before. Like a giant jigsaw puzzle, many of the original stones from the Kotel were put back in their place. Some areas, such as this directly above the Huge Stone, required additional patchwork and smaller stones were added.
The huge stone, and the intact Herodian courses beneath,
stand in mute testimony of the Midrash (Oral Tradition) explaining the verse King Solomon
wrote in the Song of Songs 2:9 "Behold, He stands behind our wall,
behind the Western Wall of the Holy Temple. Why? Because the Holy One, blessed be
He, swore that it would never be destroyed."
Shir HaShirim Raba 2:9