Adorning shorelines across the globe, lighthouses have been a common sight for thousands of years. They were important for helping ships navigate narrow straits and rocky coastlines in the dark of night. Today, lighthouses are mostly aesthetic—good for a tourist stop or a theme to decorate a room in one’s home. Yet while lighthouses have been replaced by other nautical tools such as a GPS, they continue to be an important part of sea navigation.

Before modern lighthouses, fires were built on cliffs next to reefs or rocky patches of sea. While it is not known for certain when the first lighthouse was built, the most well-known and documented lighthouse was the Pharos of Alexandria in Alexandria, Egypt, built between 285 and 247 BC.

The building was a landmark in the Port of Alexandria—it stood between 380 to 490 feet tall. The building—the prototype for all lighthouses since—was one of the Seven Wonders of the Ancient World and stood for centuries as one of the tallest manmade structures.

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 inside the structure allowed supplies to reach the top.

Most historians believe 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 is not known. 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.

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 AD, at which time an earthquake 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. The government had planned to scope the area for archeological evidence before constructing a concrete breakwater at the site.

Mr. Empereur documented hundreds of masonry blocks, as well as other statues and artifacts. Most notably, he discovered a large statue thought to be Ptolemy II—one of two statues believed to have stood at the base of Pharos. This find complemented a statue found in the 1960s thought to be Ptolemy’s wife.

The finds prompted the Egyptian government to scrap the breakwater project and instead preserve 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.