Engineering the 7 Wonders of the World: Lighthouse of Alexandria

Before modern technology existed, civilizations built incredible structures and sculptures that would live on in infamy. This is the Lighthouse of Alexandria.

The tallest lighthouse currently standing in America is only half of the size of the lighthouse built in Alexandria. It was a structure that was ultimately a first for the world, one that protected ships for up to 30 miles of the Egyptian coast. Built between 280 and 247 B.C., it is believed that the final structure was built from stone in three stacked sections. Once the Pharos Lighthouse was completed, rumors in regards to the magnitude of the lighthouse spread so quickly that artists who had never seen the structure began painting it. The completed lighthouse stood somewhere in the range of 394 and 449 feet tall for over a millennium.

After Alexander the Great died, his successor, Ptolemy, took charge to develop the city that the legendary king desired. We know that the lighthouse cost the kingdom around 800 talents, which through rough conversion we can say is equivalent to $1 billion in 2016 U.S. dollars. Light on the top of the tower was produced through the burning of gas and other tinders while it was then reflected through a series of mirrors to direct ships. Built completely out of limestone, it would have been a stunning structure, marking Alexandria on the map.

When building tall structures with stone blocks, architects and engineers are forced to drastically expand the base outward to carry the load. There would have been a lower base with a small open central core, a middle section in the shape of an octagon, and a top circular section. Given the height of the structure, modern engineers believe that the base would have been nearly a 100 foot by 100-foot square. Since the structure was built on the coast, the pounding of waves was a common and expected occurrence. To counteract this destructive act of nature, the joints of the limestone blocks were sealed with molten lead. This task likely would have taken crews many years, not only to seal but also to source the abundance of necessary metal.

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Not much is known about the specific construction processes that would have been used to lift the structure into place. Alexandria was a place of advanced engineering and technology, so scholars safely assume that pulleys and wheel systems would have been used to make the construction tasks easier.

One thing that differs from other stone structure of the time is not only the sealing of the stones with lead but also how they were locked. Each stone would have been carved with interlocking pieces, much like concrete masonry blocks are today. It’s likely that the combination of this interlocked stonework and the molten lead sealant is what allowed the stone structure to survive for so many years. Looking back, it may not seem like a structure surviving this long would be a big deal, but put it in the scope of modern skyscrapers. The lifespan of the Pharos lighthouse would be the equivalent of the empire state building lasting until the year 3481. A building lifespan of this magnitude is barely fathomable given modern construction.

The impressive stone construction on the lighthouse kept it around until it was severely damaged by earthquakes in the early 1300s. Rubble of the structure sat until 1480 when the foundation was demolished and a fort built in its place. Remains of the structure largely sat unnoticed for the next 500 years until the site was re-discovered in 1968. Even today, researchers are continuing to study rubble patterns in the surrounding waters, hoping to learn more about this ancient wonder.

Sources: NekhebetUnmuseumEncyclopedia BritannicaSoft Schools

Image Sources: [1][2]

Trevor is a civil engineer by trade and an accomplished internet blogger with a passion for inspiring everyone with new and exciting technologies. He is also a published children’s book author whose most recent book, ZOOM Go the Vehicles, is aimed at inspiring young kids to have an interest in engineering.


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