This chapter presents Mediterranean ecology as a determinant for economic performance in the ancient Greek and Roman era. It focuses on the geography, climate, environment and agriculture in the region, and health of the people and disease occurrence in the region during the ancient Greco-Roman era. The lands surrounding the Mediterranean Sea are generally hilly or mountainous. Dendrochronological evidence from the Parthenon in Athens provides evidence for a pattern of climatic variability in the fifth century BC which resembles the modern pattern. In addition to being subject to regular climatic cycles, ancient Mediterranean region was a world of sudden, unpredictable catastrophes. Mt. Vesuvius played a prominent role in the Roman period, destroying Pompeii and Herculaneum in AD 79. A combination of agricultural crops had existed in the Near East since at least circa 3000 BC. There is evidence to support that ancient populations suffered from a substantial disease burden, consisting of both endemic and epidemic diseases.