That is Trajan's Column. The inscription at its base carries letters 1900 years old that are indistinguishable from today's upper case Roman characters. In fact, a commonly used all-caps font is named Trajan. You see it everywhere, without remarking on it.
The column is a pictorial history of Emperor Trajan's military adventures. It is one of the mostly intensely studied chunks of stone in the world and has its own web site..
The slope of the ground (if any) in a square is crucial - it must never be convex. I believe that this is related to "Positive Outdoor Space" (Alexander again). A convex surface impairs the creation of positive space, and I believe that this applies in both the horizontal and the vertical plane. In this case, we seem to have a gradual, continuous slope from the right background to the left foreground. This does the square no harm.
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