Why a king studied geometry
Published: 15 May. 2025, 00:05
Updated: 15 May. 2025, 18:15
Audio report: written by reporters, read by AI
Lee Woo Young
The author is an HCMC distinguished professor at the Korea Institute for Advanced Study.
In 323 B.C., Alexander the Great died unexpectedly in Babylon on his way back from a campaign in India. Among the generals at his side was Ptolemy (367—283 B.C.), who would later rule over Egypt after the vast empire fractured into three kingdoms. Ptolemy became king of Egypt and established his capital in Alexandria, a newly built city at the mouth of the Nile. There, he founded a great library — an institution that functioned much like a modern university — and invited scholars from across the ancient world to join.
One of them was Euclid, the famed mathematician from Athens. Ptolemy summoned Euclid to the royal court and began studying geometry under his guidance. The subject, however, proved difficult. According to a widely recounted anecdote, the king eventually asked in frustration, “Is there no royal road to geometry?”
![Marble bust of Ptolemy I Soter at the Louvre Museum. [LOUVRE]](https://koreajoongangdaily.joins.com/data/photo/2025/05/15/7469d593-118a-4722-bdd1-662b97f5ea32.jpg)
The story may seem trivial at first, but it raises a deeper question: Why was a monarch so eager to study mathematics?
The answer can be traced back to Plato’s "Republic", particularly the allegory of the cave in Book VII. In that allegory, people trapped in a cave mistake shadows cast on a wall for reality, symbolizing the limitations of sensory perception. The character Socrates suggests that only through intellectual effort — particularly through mathematics — can one escape illusion and grasp true reality.
For Plato, mathematics was not merely a tool but a necessary discipline for cultivating the rational mind. In his ideal state, rulers were expected to be philosopher-kings, and knowledge of mathematics was a prerequisite. It is in this light that Ptolemy’s desire to master geometry can be understood — not as an indulgence, but as a pursuit of insight required for leadership.
Ptolemy would later be known as Ptolemy I Soter. “Soter” means “savior” in Greek. His commitment to knowledge and learning helped turn Alexandria into a beacon of intellectual life for a millennium. That legacy was no accident.
Centuries later in Korea, King Sejong displayed a similar passion for knowledge. According to the Annals of King Sejong, he studied arithmetic with court scholar Jeong In-ji. Although Sejong remarked that mathematics might seem of little use to a monarch, he nonetheless immersed himself in study.
The parallel is striking. In both East and West, leaders who earnestly pursued knowledge — particularly the abstract and difficult kind — ushered in eras of cultural and political flourishing. It is a truth that transcends time and geography.
Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
The author is an HCMC distinguished professor at the Korea Institute for Advanced Study.
In 323 B.C., Alexander the Great died unexpectedly in Babylon on his way back from a campaign in India. Among the generals at his side was Ptolemy (367—283 B.C.), who would later rule over Egypt after the vast empire fractured into three kingdoms. Ptolemy became king of Egypt and established his capital in Alexandria, a newly built city at the mouth of the Nile. There, he founded a great library — an institution that functioned much like a modern university — and invited scholars from across the ancient world to join.
One of them was Euclid, the famed mathematician from Athens. Ptolemy summoned Euclid to the royal court and began studying geometry under his guidance. The subject, however, proved difficult. According to a widely recounted anecdote, the king eventually asked in frustration, “Is there no royal road to geometry?”
Marble bust of Ptolemy I Soter at the Louvre Museum. [LOUVRE]
The answer can be traced back to Plato’s "Republic", particularly the allegory of the cave in Book VII. In that allegory, people trapped in a cave mistake shadows cast on a wall for reality, symbolizing the limitations of sensory perception. The character Socrates suggests that only through intellectual effort — particularly through mathematics — can one escape illusion and grasp true reality.
For Plato, mathematics was not merely a tool but a necessary discipline for cultivating the rational mind. In his ideal state, rulers were expected to be philosopher-kings, and knowledge of mathematics was a prerequisite. It is in this light that Ptolemy’s desire to master geometry can be understood — not as an indulgence, but as a pursuit of insight required for leadership.
Ptolemy would later be known as Ptolemy I Soter. “Soter” means “savior” in Greek. His commitment to knowledge and learning helped turn Alexandria into a beacon of intellectual life for a millennium. That legacy was no accident.
Centuries later in Korea, King Sejong displayed a similar passion for knowledge. According to the Annals of King Sejong, he studied arithmetic with court scholar Jeong In-ji. Although Sejong remarked that mathematics might seem of little use to a monarch, he nonetheless immersed himself in study.
The parallel is striking. In both East and West, leaders who earnestly pursued knowledge — particularly the abstract and difficult kind — ushered in eras of cultural and political flourishing. It is a truth that transcends time and geography.
Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
with the Korea JoongAng Daily
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