Alexandria is the second largest city in Egypt, and its largest seaport, with a population of approximately 5,000,000 people. Alexandria is home to the New Library of Alexandria and is an important industrial center of natural gas and oil pipelines from Suez. One of the Seven Wonders of the World, the Lighthouse of Alexandria, dates back to antiquity, and ongoing archaeology has revealed remains of the Ptolemaic Dynasty. Very little of the ancient city remains; much has sunk beneath the harbor due to earthquakes, and the rest has been rebuilt. Pompey's Pillar, is the most well-known ancient monument still standing. It stands on Alexandria's ancient acropolis--next to other remains. Alexandria's catacombs, known as Kom al Sukkfa, are a short distance away, consisting of a multi-level labyrinth reached via a large spiral staircase, and features dozens of chambers adorned with sculptures and burial artifacts. The most extensive ancient excavation currently being conducted is known as Kom al Dikaa, and has revealed the ancient city's well-preserved theater and the remains of its Roman baths.