Once Christianity established itself across the Roman Empire the places of worship for the followers of the new religion gradually became larger and more grand. The pinnacle of the size of the churches was of course the St. Peter’s Basilica in Rome. Here is a list of the largest Christian Cathedrals in the world.
1. St. Peter’s Basilica in Rome

built: 1506-1626
size: 15,160m2

2. Aperedica, Brazil

built: 1955-1980
size: 12,000m2

3. Milan Cathedral, Milan

built: 1386-1965
size: 11,700m2

4. Seville Cathedral, Seville, Spain

built: 1401-1538
size: 11,520m2

5. Cathedral of Saint John the Difvine, New York

built: 1892-present
size: 11,200m2

6. Basilica of Our Lady of Lichen, Poland

built: 1994-2004
size: 10,090m2

7. Abey of Santa Giustina, Italy

built: 1501-1606
size: 9,717m2

8. Liverpool Cathedral, Liverpool

built: 1904-1978
size: 9,687m2

9. Church of the Most Holy Trinity, Portugal

built: 2004-2007
size: 8,700m2

10. Basilica of Saint Paul Outside the Walls

built: 4th Century-1823
size: 8,515m2