As of the early 21st century, Christianity has approximately 2.4 billion adherents. The faith represents about a third of the world's population and is the largest religion in the world. Christians have composed about 33 percent of the world's population for around 100 years. The largest Christian denomination is the Roman Catholic Church, with 1.17 billion adherents, representing half of all Christians.

How long have Christians made up nearly 1/3rd of the population?