Ancient Pergamum is located on the plains and foothills along the Caicus River in Western Turkey. It was considered a major city in Asia Minor since the 3rd century BC, and became a Greek and Roman hub for worshipping Aesclepius, the god of healing, and Serapis, the Egyptian god of the underworld. The ruins of ancient Pergamum include the acropolis, the worship complexes known as the Aesclepium and Serapeum, and the incredible 10,000-seat amphitheatre built into the side of a steep hill. The marble Temple of Emperor Trajan from the second century AD has also been excavated and restored. The Trajan complex includes a huge library, the second largest after Alexandria, Egypt in the ancient world.