Historian Simon Sebag Montefiore uncovers the central role played by religion in creating and maintaining the power of the city of Rome from its foundations to the modern day. From its founding myth and its pagan gods whose actions dictated the politics of ancient Rome to the time that a new cult from the East, Christianity, threatened the status quo. In the first episode we see how every event in ancient Rome revolved around religion. From the foundation myth through to the deification of Emperors; nothing could happen without calling upon the Pantheon of Roman gods. Simon investigates how the Roman's worshipped and sacrificed to the gods. He discovers that sacredness defined what was Roman and it was the responsibility of every Roman to play their part in the cult.

Rome casts aside its pantheon of pagan gods and a radical new religion takes hold. Christianity was just a persecuted sect until Emperor Constantine took a huge leap of faith, promoting it as the religion of Empire.

Simon Sebag Montefiore charts Rome's rise from the abandonment and neglect of the 14th century into the everlasting seat of the papacy recognised today. His story takes us through the debauchery and decadence of the Renaissance, the horrors of the Sack of Rome and the Catholic Reformation, through to the arrival of fascism and the creation of the Vatican State.