I remember that my mathematical education started with numbers. First, my father, then later, my elementary teacher, taught me how to count as my elementary math education. However, 2400 years ago, everything was utterly different, and kids were taught geometry first.
Before Jesus, geometry was more important than numbers. For instance, when the founder of the first institution of higher education in the Western world, Plato, came back to Athens, he decided to found the “Academy,” which would be the intellectual center of the world. For that purpose, instead of taking a nonrefundable application fee, he engraved “ΑΓΕΩΜΕΤΡΗΤΟΣ ΜΗΔΕΙΣ ΕΙΣΙΤΩ” (Translated from Greek as “Let no man ignorant of geometry enter.”) at the door of his academy to eliminate those who were opposed.
Plato’s idea of the ideal world had a strong connection with beauty and intelligence, both well taught in mathematics. Later, a young man, Euclid of Alexandria, entered that door and became a mathematician and philosopher, and wrote an astonishing geometry book, The Elements. Euclid’s Elements is the most famous textbook of all time and the most widely printed text after the Holy Quran and the Holy Bible.
The Elements was so influential because it contained a comprehensive collection of important works in mathematics up until Euclid’s time. Most of Euclid’s ideas came as revelations and laid the foundation for Euclidean Geometry. These ideas became the core of the teaching and understanding of geometry for over two thousand years up until today. You were not viewed as educated for a long time if you had not read The Elements. Even today, when you read The Elements, it contains modern theories that remain relevant even today, which makes it extraordinary.