Adorning coastal shorelines across the globe, lighthouses have been a common sight for centuries. For most, lighthouses have become merely aesthetic, good for a tourist stop or a theme to decorate a room in one’s home. While lighthouses have been partially replaced by other nautical tools, such as a global positioning system (GPS), they continue to be an important part of sea navigation.

Before modern lighthouses, fires were built on cliffs, warning of reefs or rocky patches of sea. While we cannot know for certain the exact date of the first lighthouse, the most well-known and documented lighthouse was in Alexandria, Egypt, built between 285 and 247 B.C.

The Pharos of Alexandria, the landmark for the port of Alexandria, stood between 380 to 490 feet tall, and later served as its lighthouse. The building—the prototype for all lighthouses since—was one of the Seven Wonders of the Ancient World and stood as one of the tallest manmade structures on earth for centuries.

Thought to be commissioned by Ptolemy I Soter, a general of Alexander the Great, and later finished by his son, the lighthouse was built in three sections that sloped in slightly: (1) a rectangular base, (2) an octagonal mid-section and (3) a cylindrical top. A spiral ramp on the inside of the structure allowed supplies to reach the top.

Most historians agree that the Pharos used mirrors, either polished bronze or silver-backed glass, to reflect the light of a fire from the peak of the spire. However, the exact technology used has been lost to time. Some accounts say the fire could be seen as far as 35 miles away! Other unconfirmed legends claim that the Pharos’s beacon could be focused and used to set fire to enemy ships.

In order to withstand blows from the ocean’s waves, the light-colored bricks were held together by lead mortar. This allowed the structure to stand well into the 14th century A.D., when an earthquake damaged it for a third time and reduced it to rubble. A fort was later built on the site, and it remains today.

Romance languages often get their words for “lighthouse” from Pharos itself. In French the word is phare. In Spanish, faro.

In 1994, archeologist Jen-Yves Empereur was asked by the Egyptian government to study the seabed around the area where the lighthouse was once located, before constructing a concrete breakwater at the site.

Mr. Empereur documented hundreds of masonry blocks, as well as other statues and artifacts—most notably a large statue, thought to be Ptolemy II—one of two statues believed to have stood at the base of Pharos. This find complimented a statue found in the 1960s thought to be Ptolemy’s wife, and the Egyptian government decided to scrap the breakwater project, instead preserving the site as an underwater park.

Today, divers over the age of 18 can swim through the site to see sphinxes, statues and other remains of what was once one of the Wonders of the Ancient World.