Final answer:
The Great Altar of Zeus and Athena in Hellenistic Greece was made of marble, chosen for its workability and durability. Few bronze originals have survived, as they were often melted down, leaving mostly Roman marble copies for historical reference.
Step-by-step explanation:
The form of the Great Altar of Zeus and Athena in Hellenistic Greece is made of marble. Greek sculptors primarily used bronze for their original works. However, due to the value of bronze and its reuse especially during war times, many of these were melted down. Consequently, what survives today are often marble Roman copies of the original Greek bronzes. For monumental pieces like the Great Altar of Zeus and Athena, marble was the stone of choice, as evidenced by Figure 9.5.9, which shows the east frieze of the Altar of Zeus, and also by the process described for creating Greek marble sculptures.
The Great Altar, located in Pergamon (modern-day Bergama, Turkey), is well-known for its grand design and for its frieze, which is a vivid representation of the Gigantomachy. The altar itself was a U-shaped Ionic building built on a high platform with central steps leading to the top, as seen in Figures 9.5.6 and 9.5.7. It was a marvelous example of Hellenistic art that displayed the drama and pathos characteristic of the era.