This document summarizes many important ancient Greek festivals and religious celebrations. It describes festivals dedicated to major Greek gods like Zeus, Poseidon, Apollo, Athena, Demeter, Dionysus, and Aphrodite. For each festival it provides the name, date, location, key activities, religious significance, and purpose. The largest and most important festivals included the Olympic Games, Panathenaea, Dionysia, Eleusinian Mysteries, and others. Rituals typically involved sacrifices, processions, competitions, and ceremonies to honor the gods and mark changing seasons.