Castel Sant'Angelo
I don't know if it's a blemish on a city with so much beautiful art or if I should take it as another piece of history that's worth investigating. The emperor Hadrian decided that he wanted his remains buried in a garden that had long belonged to the imperial family and joined the garden to the land with a bridge known at the time as Elio. If you visit the interior, specifically the Treasure Room, you'll be in the heart of the mausoleum where the remains of the emperor were buried. Emperors continued to be buried there up until Caracalla, the last emperor to be buried there before the building was converted into a fortress.