The Qaitbay Fortress, also known as the Citadel of Qaitbay, is a 15th-century defensive fortress located on the Mediterranean coast in the city of Alexandria, Egypt. It was built by Sultan Al-Ashraf Qaitbay in 1477 AD on the site of the ancient Lighthouse of Alexandria, one of the Seven Wonders of the Ancient World.

The Lighthouse of Alexandria, also known as the Pharos of Alexandria, was one of the Seven Wonders of the Ancient World. It was a monumental structure located on the eastern tip of the Pharos Island, which was then separated from the mainland by a narrow channel. The lighthouse was built in the 3rd century BC during the reign of Ptolemy II Philadelphus, and was designed by the architect Sostratus of Cnidus.

The Lighthouse of Alexandria was a marvel of ancient engineering, standing at an estimated height of between 115 and 135 meters (377-441 feet), making it one of the tallest structures of its time. It was constructed of white marble blocks and was topped with a bronze statue of the god Zeus or another deity.

The lighthouse was used primarily as a navigational aid for ships entering the harbor of Alexandria. It was equipped with a mirror that reflected sunlight during the day and a fire that was lit at night, which could be seen from as far as 50 kilometers (30 miles) away. The light from the lighthouse was said to have been so bright that it could burn ships that came too close to the shore.

Over the centuries, the Lighthouse of Alexandria was damaged by earthquakes and other natural disasters, and was eventually destroyed in the 14th century AD. Today, only a few ruins and artifacts remain, including some marble blocks that were discovered in the harbor during the 1990s.

Despite its destruction, the Lighthouse of Alexandria remains an iconic symbol of ancient engineering and maritime history. Its influence can be seen in lighthouses and other navigational aids that are still used today.

The fortress was built in response to threats from the Ottoman Turks, who had recently conquered Constantinople (modern-day Istanbul) and were expanding their empire into the eastern Mediterranean. The fortress was designed to protect Alexandria and its port from invasion and attack, and was built using the latest military technology of the time.

The Qaitbay Fortress is a massive stone structure, with walls that are over 2 meters (6.5 feet) thick in some places. It is surrounded by a moat, which was filled with seawater from the Mediterranean. The fortress has several towers and bastions, including the famous “Round Tower,” which offers panoramic views of the city and the sea.

Over the centuries, the Qaitbay Fortress has been used for a variety of purposes, including as a military base, a prison, and a customs house. Today, it is a popular tourist attraction and is considered one of the most important historical sites in Alexandria. Visitors can explore the fortress and learn about its fascinating history, as well as enjoy the stunning views of the city and the sea.