Persia was a land that included parts of what are now Iran and Afghanistan. The map above shows the Achaemenid Empire at its peak in 500BC. It was the center of an empire that stretched west to the central Mediterranean Sea, east to India, and from the Gulf of Oman in the southern Russia in the north. Persia is one of the world's most mountainous countries. Its mountains have helped to shape both the political and the economic history of the country for several centuries. The mountains enclose several broad basins, or plateaus, on which major agricultural and urban settlements are located. There are no major river systems in the country, and historically transportation was by means of caravans that followed routes traversing gaps and passes in the mountains. The mountains also impeded easy access to the Persian Gulf and the Caspian Sea.