I watched how the Alexander Column was made.
So, in the open space next to the installation site of the column on a special not high pedestal in the form of a row of slingshots (similar to anti-tank hedgehogs) there is a tube - a rod, black, very similar to graphite from a pencil. Several people work about 3 meters tall, dressed in blue overalls.
Then special. the machine moves along this rod and wraps it with some kind of plastic mass, in the form of a flat tape. This is exactly the same as in our time pipes are wrapped with insulation, only this "insulation" does not overlap, but exactly end-to-end. Something like this:
At the end of the passage along the entire length, the car stops, waits a little, and goes in the opposite direction. During the waiting period, the mass hardens and the next layer is already applied to it. Gradually, layer by layer, the rod increases in volume and reaches the diameter that we already know. The last pass of the machine "slider" adheres tightly to the column (very similar to the skin) and moves more slowly using water. This is the last stage - grinding and polishing.
Then one end of the column is somehow lifted, but there are no ropes. Some kind of energy from above. The column rises, and its lower end exactly fits into the prepared recess. After that, a pyramid is erected around the column of bricks, the inner walls of which are lined with a metal grid-lattice in the form of hexagons. The pyramid is truncated, just at the level of the top of the column.
There is no sculpture, just a flat surface. At the base of the column, a wire is connected to the graphite rod, which connects to the grid inside the pyramid. That's all I could see.
Promotional video:
In order to accurately disassemble the pyramid without damaging the column, scaffolding was placed. The pyramid was dismantled (not destroyed, but dismantled) from top to bottom. The figure shows the stage of not complete disassembly of this pyramid.
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Apparently, the column was a battery powering the entire complex, and Montferrand destroyed the pyramid, de-energizing and destroying the structure. Now it is clear where he got the idea to make the column hollow - he saw a graphite rod, which he wanted to hollow out.
Friend's comment:
It was a phased array radar system, that is, without rotating parts for monitoring territories and outer space, something like this:
And the column was really a battery, because any technique requires power. It was a large complex of structures, incl. and projecting a pure field hologram so that there is no temptation to attack. The large complex of energy facilities involved the Hermitage with its columns and sculptures on the roof, and St. Isaac's Cathedral with its many columns. Everything had a purpose.