Euclid, sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referred to as the “founder of geometry” or the “father of geometry”. He was active in Alexandria Mediterranean port city in Egypt, during the reign of Ptolemy I (323–283 BC).
Greek mathematician
Euclid, sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referred to as the “founder of geometry” or the “father of geometry”. He was active in Alexandria Mediterranean port city in Egypt, during the reign of Ptolemy I (323–283 BC).
Born: 325 BC
Died: 270 BC, Alexandria, Egypt

Euclid authored the Elements, the most famous and most published mathematical work in history; another great work, Optics, explained light’s behaviour using geometrical principles – the basis of artistic perspective, astronomical methods, and navigation methods for more than two thousand years. Enormously influential in mathematics teaching for over two thousand years, the Elements provided the spark that inspired many of the world’s greatest mathematicians and scientists to embark on their remarkable intellectual journeys. In the Elements, Euclid deduced the theorems of what is now called Euclidean geometry from a small set of axioms. Euclid also wrote works on perspective, conic sections, spherical geometry, number theory, and mathematical rigour.

Little is known about Euclid personally and we do not know what he looked like. He was born in around 325 BC, was probably educated in Plato’s school in Athens, and he taught mathematics in Alexandria, the great new city of commerce and academia constructed in Egypt on the orders of Alexander the Great during Euclid’s lifetime. Euclid’s arrival in Alexandria came about ten years after its founding by Alexander the Great, which means he arrived c. 322 BC.
Euclid’s Elements
Euclid’s Elements is a masterpiece, a work of genius whose importance to the intellectual development of our species is difficult to exaggerate. It inspired ancient Greeks, such as Archimedes; Persians, such as Omar Khayyam; and, following the Renaissance, thousands of individual scientists such as Nicolaus Copernicus, Galileo Galilei, Isaac Newton, James Clerk Maxwell, Albert Einstein, and Thomas Gold.
Working in Alexandria, Euclid compiled mathematical proofs from the Pythagoreans, Hippocrates, Theudius, Theaetetus and Eudoxus. In all, it contains 465 theorems and proofs, described in a clear, logical and elegant style, and using only a compass and a straight edge. and other earlier Greek mathematicians, strengthened the logical rigour anywhere it was weak, added his own proofs, and produced a work of stunning intellectual power.Euclid was not concerned with solving mundane problems in mathematics such as how many tiles you need to cover a roof. His goal was to discover eternal, universal truths.
Starting with a few self-evident principles, such as that all right-angles are equal, Euclid deduced and proved a large number of ever more sophisticated mathematical theorems placing them in the Elements’ 13 books.The Elements deals with three fields:
Chapters 1-6: Plane geometry.
Chapters 7-10: Arithmetic and number theory.
Chapters 11-13: Solid geometry.

It includes an extraordinarily beautiful proof that there are infinitely many prime numbers.also includes the first ever nontrivial mathematical algorithm, perhaps devised by followers of Pythagoras, which Euclid uses to calculate the greatest common divisor of two numbers.
Euclid’s Optics
Euclid’s Optics was an immensely influential book on light and vision. Euclid explained light’s behaviour using geometrical principles he had developed in the Elements. His theory of light was the basis of artistic perspective, astronomical methods, and navigation methods for more than two thousand years.
Euclid considered the geometrical behaviour of light rays. He got one major point wrong – he adopted the Greek consensus view of the time that we see things because our eyes emit rays rather than receive rays. Nevertheless, Euclid’s theory of light works perfectly well, because as can be seen in the image below, it is the geometry that is important, not whether a ray is travelling into or out of an eye.

One of Euclid’s geometrical diagrams from Optics. Using arguments based on this diagram, Euclid establishes that when viewed from different locations, objects of equal height on a flat plane can appear to be of different height.
The Papyrus Oxyrhynchus 29 is a fragment of the second book of the Elements of Euclid, unearthed by Grenfell and Hunt 1897 in Oxyrhynchus.The fragment contains the statement of the 5th proposition of Book 2, which in the translation reads:
If a straight line is cut into equal and unequal segments, the rectangle contained by the unequal segments of the whole together with the square on the straight line between the points of the section is equal to the square on the half.
In addition to the Elements, at least five works of Euclid have survived to the present day. They follow the same logical structure as Elements, with definitions and proved propositions.
Data deals with the nature and implications of “given” information in geometrical problems; the subject matter is closely related to the first four books of the Elements.
On Divisions of Figures, which survives only partially in Arabic translation, concerns the division of geometrical figures into two or more equal parts or into parts in given ratios. It is similar to a first-century AD work by Heron of Alexandria.
Catoptrics, which concerns the mathematical theory of mirrors, particularly the images formed in plane and spherical concave mirrors. The attribution is held to be anachronistic however by J J O’Connor and E F Robertson who name Theon of Alexandria as a more likely author.[21]
Phaenomena, a treatise on spherical astronomy, survives in Greek; it is quite similar to On the Moving Sphere by Autolycus of Pitane, who flourished around 310 BC.
Optics is the earliest surviving Greek treatise on perspective. In its definitions Euclid follows the Platonic tradition that vision is caused by discrete rays which emanate from the eye. One important definition is the fourth: “Things seen under a greater angle appear greater, and those under a lesser angle less, while those under equal angles appear equal.” In the 36 propositions that follow, Euclid relates the apparent size of an object to its distance from the eye and investigates the apparent shapes of cylinders and cones when viewed from different angles. Proposition 45 is interesting, proving that for any two unequal magnitudes, there is a point from which the two appear equal.
Other works are credibly attributed to Euclid, but have been lost. Lost works include books on conic sections, logical fallacies, and “porisms.”

The ancient Egyptians knew a lot of geometry, but only as applied methods based on testing and experience.Ancient Babylonians also knew a lot of applied mathematics, including the Pythagorean theorem. Archaeological excavations at Nineveh discovered clay tablets with number triplets satisfying the Pythagorean theorem, such as 3-4-5, 5-12-13, and with considerably larger numbers. As of 2006 CE, 960 of the tablets had been deciphered.