By the fourth century, it was the main religion of the Roman Empire. It spread to the rest of Europe in the Middle Ages, with minority pockets of worshippers in the Middle East, Northern Africa and parts of India. Following the Age of Exploration, beginning in the 15th century, Christianity spread to the Americas and Australasia.
As a result of its global growth, it had an almost unparalleled influence on the development of Western civilisation. But since the Enlightenment and the dawn of the Modern Era, secularism and rationality have challenged Christianity’s orthodoxy and adherence to the religion in Europe dropped off. However, its position in North America and in many parts of Africa remains strong. At the dawn of the 21st century, worldwide followers stand at about 2.2 billion.