There were a great many different religions followed in the ancient and medieval time periods. Some of them are still practiced today; others are not. It is hard even to know what religion is, but we see religion as any tendency to change your own behavior in accordance with supernatural forces.
Most people in the ancient and medieval world believed that there were many unseen spirits affecting how things happened. The earlier faiths all thought that there were many gods, each responsible for different things: a god of the sky, a god of water, a god of love, and so forth. Egyptian, Sumerian, Chinese, Indian, African, Greek, Roman, and German religions all had their gods organized this way, even though they had different gods. We call this polytheism (poll-ee--THEE-is-em). Beginning at least with the beginning of farming, if not before, many people all over the world thought you had to keep these gods happy with animal sacrifices - killing animals for the gods.
But, beginning about 1350 BC in Egypt, there was a movement toward monotheism, or just believing in one god (often with a lot of weaker helper gods or angels). Akhenaten, an Egyptian pharaoh, may have been one of the first powerful people to push this idea. By 1100 BC or so (maybe), we see the Jews practicing monotheism.
Around the same time, Zoroastrianism swept West Asia with the same idea, adding a strong notion of dualism, with the world divided into good and evil. Belief in an afterlife, and increasingly in an afterlife where you would be judged good or evil, spread from Egypt through West Asia to India, in the form of reincarnation. The afterlife also reached Greece, as we see in the stories of Persephone and Achilles, but never had much impact on Roman religion.
Not long afterwards, about 500 BC, as the first big empires got started with the Assyrians and then the Persians, the world's religious leaders responded with a wave of new, big, sweeping religions. The earliest was Buddhism, in India. East Asia saw the rise of Taoism and Confucianism. Judaism developed more formal structure under Ezra and Nehemiah. In Greece, this phase brought us first Socrates and then Plato. Christianity spread west with the Roman Empire.
By 300 BC, in India, animal sacrifice was beginning to seem old-fashioned and yucky. Most Hindus became vegetarians, and they sacrificed little cakes, rather than animals. Christians, in the first century AD, replaced animal sacrifice with Communion, and the Jews stopped sacrificing after the Romans destroyed their temple. Romans themselves soon began to sacrifice mainly by throwing incense, rather than animals, into the fire. Christianity spread monotheism west to the Mediterranean and Europe. By the 500s AD, Buddhism correspondingly spread east all over China and Japan. And in the 600s AD, Islam - even more monotheistic, even more abstract - replaced Christianity and Zoroastrianism as the main religion followed in the Mediterranean, West Asia, and much of Africa. By the 1200s, Islam reached India too.
Learn by doing: visit the services of a religion you're not familiar with
More history of religion
(with Egyptian Religion)
West Asian Religion
Cool stuff we've been enjoying: Looking for birthday gifts? Check out these new Chromebooks - all the computer you need for only $229.00!. Then study in peace with these Beats wireless headphones - for the exact same price! When you're done, show off your presentation or watch a movie with this excellent smartphone projector for only $39.99!