Trade was critical for any ancient empire to survive. Certain geographic areas had certain resources in abundance, while others were sorely lacking. The Greek city states exported resources such as silver, obsidian and seashells, and also crafts such as pottery and metal vases. However, they imported other resources such as copper, tin, gold and amber, and other products, such as glass beads and seals. Cities along trade routes, such as Alexandria in Egypt and Byblos in the Middle East, became wealthy and powerful.