Historically, evidence of atheistic viewpoints can be traced back to classical antiquity and early Indian philosophy. In the Western world, atheism declined after Christianity gained prominence. The 16th century and the Age of Enlightenment marked the resurgence of atheistic thought in Europe. Atheism achieved a significant position worldwide in the 20th century. Estimates of those who have an absence of belief in a god range from 500 million to 1.1 billion people. Atheist organizations have defended the autonomy of science, freedom of thought, secularism, and secular ethics.