He was born in modern-day Libya in 276 BC. A brilliant mathematician, mapmaker and poet, Eratosthenes rose to prominence in Egypt as the third curator of the Great Library of Alexandria. At its zenith, the Library housed more than one million books or scrolls – the stored knowledge of the known world.
More than today’s concept of libraries, the Great Library was a gathering place for the finest minds of its day. There were dissecting rooms for medical experiments, an observatory for charting the stars, debate rooms for politics and government, and shelves overflowing with books deciphered by dozens of scriveners to translate each scroll into all major written languages. In this stimulating intellectual environment, Eratosthenes made one of the most remarkable discoveries of all time, and he did it without technology.
Eratosthenes knew that in the area of modern-day Aswan on the Tropic of Cancer, the noon-day sun would be exactly overhead at the summer solstice. Therefore, he reasoned, a long stick or obelisk planted in the ground at that location at noonday should cast no shadow. He sent his associate to pace off the entire 800 kilometers between Alexandria in the north and Aswan in the south.
When the associate arrived in Aswan, he planted an obelisk to observe the shadow upon it at the appointed hour. At the same time, Eratosthenes planted an identical-length obelisk in Alexandria and recorded his observations in the north. Reuniting later, the two men compared notes. They discovered that the shadow on the Alexandria obelisk at noon-day was lengthy, while the Aswan obelisk to the south cast no shadow at all (as expected).
Pondering these results, Eratosthenes concluded that if the Earth were flat, the shadows cast upon the obelisks should be approximately equal. However, if one were to take a piece of flat paper and poke two sticks through it at each end, then bend the paper downward at one end so the middle of the paper bows slightly upward, the sun would cast different-length shadows upon the sticks connecting the curved paper. The length of shadows produced would depend upon the angle of the sticks relative to the curvature of the paper.
Therefore, the only explanation for the lengthy shadow on the Alexandria obelisk was that the Earth is curved. In fact, from the shadow’s length, Eratosthenes measured a seven-degree angle relative to the Aswan obelisk. In other words, if one were to drill down to the center of the Earth, the two obelisks planted 800 kilometers apart would eventually intersect at a seven degree-angle.
Recognizing that seven degrees is a little more than one-fiftieth of a 360-degree circle, Eratosthenes correctly concluded that the Earth’s circumference is approximately 41,000 kilometers: 360 divided by 7 times 800 kilometers. So accurate was his estimate that it took modern-day satellites to improve on the actual circumference he calculated. Two sticks, a friend’s feet, Eratosthenes’ brain, and voil: The Earth is round; and oh-by-the-way, it is 41,000-plus kilometers in circumference, give or take!
God endowed man with a marvelous brain. When we apply critical observation and thought to the deepest problem, we have the capacity to achieve results that surprise and delight. The ancients would have been in awe at the miracle of radio, television, electronics and space flight, but they were on equal footing when it came to problem-solving and brain power.
The Great Library eventually burned to the ground, and with it, all of its stored knowledge, including precious translations of Ancient Egyptian into Greek (lost until the discovery of the Rosetta Stone in 1799). Eratosthenes teaches us that whatever the obstacle, there is no unsolvable problem – only visionless men.
But perhaps the most valuable lesson from the ancients is not found amid the ruins of man’s doomed creations. The Great Library of Alexandria, as remarkable as it was, never contained the power to exalt mankind or to fill the measure of our creation. Only Jesus could accomplish that. All of man’s achievements are for naught if we fail to acknowledge the source of our wisdom and the purpose of our creation. “What is man that thou art mindful of him? … For thou hast made him a little lower than the angels…” (Psalms 8:4-5).
Given the natural man’s tendency to reject God whenever our brazen towers rise as tall as our egos, we often fall prey to idolatry like the Children of Israel: “who worshipped and served the creature more than the Creator” (Rom. 1:25). Though it is challenging for some to acknowledge God’s hand in any human achievement, just as the “eye cannot say unto the hand, I have no need of thee” (1 Cor.
12: 21), so man will never outgrow his Creator.
