Trade was critical for any ancient empire to survive. Certain geographic areas had certain resources in abundance, while others were sorely lacking. Atlantis ferried supplies from its vast stores to its most distant colonies. 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.