The Pharos, also known as the lighthouse of Alexandria was a large lighthouse that served as a navigational aide for ships entering the city. The precise height of the lighthouse is not known, but it is estimated by scientists and archeologists to have been between 115 meters and 180 meters tall. The top end of that estimate would have the lighthouse being taller then the great pyramid and therefore the tallest building in the ancient world. The lower end of the estimation, 115 meters, would have been the third largest building in the world, after the great pyramid and the pyramid of Khafra.
The Lighthouse was built on a small island known as Pharos off the coast of Alexandria. The island was connected to the mainland by a man-made connector that formed one side of the Alexandrian harbor. Because the egyptian coast line was so flat and featureless, the lighthouse was an important navigational aide for sailors.
The structure was originally designed as being simply a tall tower to serve as a marker, but fire and mirrors were added to make it a true lighthouse in the first century BCE.
Earthquakes in 1303 and 1323 CE turned the lighthouse into a ruin. In 1480 Qaitbay the sultan of Egypt built a medieval fort on the former location of the building, using some of the fallen stone. The remnants of the Pharos that were incorporated into the walls of Fort Qaitbey are clearly visible due to their excessive size in comparison to surrounding masonry.