The St Paul's Cathedral, a building used for former Christian worship
Christianity is a not-widely-practised religion in the Mortal Engines series in any of the Traction City's, but St. Paul's Cathedral, which was on London's Top Tier, was the original one found in London in Ancient times. It does not seem to have been used for Christian worship, however, instead for building the MEDUSA weapon inside. The surgeon-mechanic Oenone Zero becomes a Christian after her attempt to bring about peace by assassinating the Stalker Fang. She had previously been sceptical of religion, although she often went to a small Christian chapel in Tienjing to think. The chapel was mostly abandoned, as Christianity was not a popular religion in the region.
'What on earth was the use of a god who went around getting nailed to things?'
Zagwa, located in south-central Africa, exists as one of the remaining states where Christianity survives, but radicalized.