Two of the most powerful empires in the ancient world were Greece and Rome. It's impossible to understand these empires without understanding the religions that were so important to them. Religion wasn't simply a part of the lives of the ancient Greeks and the ancient Romans; religion was the lens through which they understood the universe and all the events within it. Although the religions of the ancient Greeks and Romans are virtually extinct in their original forms, they live on in the cultures, imaginations, and even the religions of the modern western world.
In the ancient world, "religion" and "philosophy" were not completely distinct entities. The beliefs of the average Greek or Roman might have been influenced both by traditional beliefs about the gods and ideas derived from the teachings of the philsophers. In addition, philosophers like Plato and Socrates addressed the subjects we often group under "religious" today, such as the meaning of life, the existence of an afterlife, the nature of the universe, and the nature of gods.