If you were anyone of importance in Rome and died between 24 B.C.E. and 98 B.C.E. you were buried in here. Occupied by the Colonna family in the Middle Ages, the Mausoleo was fortified and converted into part of the Castel Sant'Angelo. Yes, they lived with dead people.
After the humiliating defeat of the Commune of Rome in 1167, the Colonna family was disgraced, banished from the city and their fortification was dismantled. Later, the family was allowed back into Rome and spent the duration of the Renaissance feuding with the rival Orsini family. If this teaches us anything, it's that if you want to get rid of someone, hang them, because banishment is far too temporary.