A massive drum-shaped structure overlooking the Tiber river near the Vatican; Castle Sant’Angelo.
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Originally the mausoleum, then transformed into a fortress, prison, and now a historical attraction that pulls millions of tourists every year.
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It was commissioned by Emperor Hadrian in 135 AD as a grand mausoleum for himself and his family.
The architect is believed to be Demetriano, a Greek engineer. Inspired by Roman imperial style, the design featured a circular drum atop a square base, once crowded with a bronze statue and encircled by a garden and golden quadriga - an architectural form that symbolized eternity and imperial power.