The Frangipani family in Rome, for instance, possessed the Colosseum from 1200 and fortified it as a castle, using it to control approaches to the Lateran Palace, and therefore could protect (or imprison) the pope and papal offices. They lost control of it to the growing Annibaldi family in the mid-13th century (who had popes Gregory IX and Alexander IV on their side). When the papacy moved to Avignon (1309 - 1377), access to the Lateran wasn't so important, Roman population declined, and the Colosseum was abandoned.
The Frangipani were Guelphs, more interested in supporting the pope's power, rather than Ghibellines, who supported more authority for the Holy Roman Emperor. They claimed ancient roots, but they do not appear in records prior to 1014. They involved themselves in many papal conflicts, such as the Investiture Controversy between Gregory VII and Holy Roman Emperor Henry IV. They reached their peak of influence when they got Pope Honorius II elected.
There were many branches of the family—such as in Friuli and Dalmatia—but the Roman branch ended in 1654 with the death of Mario Frangipani.
One of the least admirable actions by a Frangipani was in 1268 when Giovanni Frangipane betrayed the last of the Hohenstaufen dynasty, the teenage Duke of Swabia. I'll tell you about poor Conradin tomorrow.