Under the Ptolemies, the port city of Alexandria became the premier city of the Hellenistic world. It was a dynamic cosmopolitan city that by the end of the first century B.C. boasted almost one million inhabitants. Alexandria was a bustling port city where the main enterprise was the pursuit of wealth. The harbors were busy and the markets thronging, and international bangs grew to serve the people. To make sure ships could enter the port safely, Hellenistic scientists built a huge lighthouse on an island (Pharos) outside the harbor. The structure was 440 feet high, and the light from the lantern at the top was intensified by a system of reflectors. Ships approaching the harbor were guided by the beam of the lighthouse that was looked on as on of the seven wonders of the ancient world.