This imposing mediaeval tower is annexed to Mercati di Traiano and is not only one of the oldest and most fortified towers in Rome but also qualifies as the tallest. You'll notice it tilting slightly due to an earthquake in 1348 that caused the top floor to crumble. Despite popular belief indicating Nero in its construction, the more probable reality points to Pope Innocent III as its commissioner. People just assumed Nero because it's big and gaudy. I can't blame them.
During the Renaissance, there were rumors of a treasure in the hard-to-reach upper levels, but no proof was ever found.