The international trade in church bells marks the beginning of a new age for Christianity, one with Africa at its core.

"Our bells are like the thermometer of the faith… Through our trade, we can immediately understand where the faith is most alive, and where it is waning," says Armando Marinelli, an artisan church bell-maker from Italy.

"We currently have orders from Tanzania, Nigeria, [Democratic Republic of] Congo... So we can tell that, whereas faith here in Italy is a bit up and down, in Africa it's thriving."

His foundry, Campagne Marinelli, is centuries old, and bells made there hang in some of Italy's most well-known locations, including the Vatican's St. Peter's Square and the Leaning Tower of Pisa.

The declining popularity of Marinelli bells in homes now mirrors the fall of Christianity in western Europe, historically the center of the religion.

The Marinelli bells are therefore sent across the oceans rather than being placed in adjacent residences.

We tracked the Marinelli bell to Odoni in south-western Nigeria for a BBC World Service documentary where we discovered a vibrant Christian community.

"The bell, we see it as the voice of God… the church in Africa is booming," announces Father Cletus, the parish priest.

"We believe the re-evangelisation of the Earth is going to happen from sub-Saharan Africa, Nigeria in particular," agrees Pastor Paul Enenche of Dunamis International Gospel Centre.

"Believe in that!"