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A closer view of the cylindrical tower that was constructed on top of the square base. View looking southwest.
It appears that the cylindrical tower was not integrated into the square base, but that it was constructed on top of it.
There actually is an outer “cylinder” that is constructed around a round central column and stairs are wedged in between the two parts. The round central column is visible behind and to the right of the woman in the picture. She is about 5 ft. 9 in. [1.7 m.] tall.
Note the exterior construction visible in the lower left portion of the image that was built up against the cylindrical tower.