Why were some ancient Greek stadiums built into hillsides?

Ancient Greek stadiums were often built into hillsides to utilize the natural slope of the terrain for spectator seating. By cutting the structure into a hill, architects could create massive, sloping embankments that provided a large seating capacity without the need for complex, free-standing support structures.12

This design approach was a practical and efficient way to accommodate thousands of spectators, as seen at sites like Olympia, Thebes, and Epidaurus. While later Roman architecture often favored free-standing structures—such as the amphitheatre—the use of natural topography remained a defining characteristic of early Greek athletic and theatrical architecture.13