50 free Euclid trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Almost nothing is known about Euclid the man, but everything is known about his book, and this quiz covers both: the geometer of Alexandria around 300 BC, the thirteen books of the Elements, the five postulates and five common notions, the proof that primes never run out, the algorithm still used to find greatest common divisors, and the two thousand years of translations, printings and rebellions that followed. Easy questions ask what Euclid is called and what his famous book is named; harder ones dig into the philosopher he was long confused with, the pons asinorum, the first printed edition of 1482, Oliver Byrne's coloured Euclid, the mathematicians who broke the parallel postulate and the space telescope that carries his name. It suits maths teachers and students, history-of-science fans and quiz nights that want a science round with a classical flavour. Every answer has been checked against the Wikipedia articles on Euclid, the Elements and the geometry that grew from them, and each question shows its source once you have answered.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Euclid is traditionally known by what title?
The father of geometry
His system dominated the field until the early 19th century and is still called Euclidean geometry.
Q 02What is the Greek title of Euclid's great treatise, the Elements?
Stoicheia
By metonymy "Euclid" can simply mean the book itself, or geometry in general.
Q 03How many books make up the Elements?
Thirteen
Books 1 to 6 cover plane geometry, 7 to 10 number theory and 11 to 13 solid geometry, roughly speaking.
Q 04In which city is Euclid generally accepted to have spent his career?
Alexandria
He may have been among the first scholars of Ptolemy I's Musaeum, and Apollonius later studied with his pupils there.
Q 05Under which ruler's reign did Proclus place Euclid's activity?
Ptolemy I
Ptolemy ruled from about 305 to 282 BC and built the Musaeum, Alexandria's great centre of learning.
Q 06What is Euclid's famous reply when the king asked for a quicker way to learn his subject?
"There is no royal road"
The anecdote is doubtful; a near-identical story is told about Menaechmus and Alexander the Great.
Q 07Which two ancient scholars are the main sources for the traditional account of Euclid's life?
Proclus and Pappus
Both wrote many centuries after Euclid; Proclus's commentary on Book I dates from the 5th century AD.
Q 08With which earlier thinker was Euclid long confused by medieval and Renaissance scholars?
A Socratic philosopher from Megara
The Socratic philosopher reportedly sneaked into Athens dressed as a woman to hear Socrates; the mix-up put "Megarensis" on early printed editions.
Q 09What does the Greek name Eukleides mean?
Renowned or glorious
It combines eu- (well), klês (fame) and the suffix -ides (son of).
Q 10Medieval Arabic sources, considered unreliable, claimed Euclid was born in which city?
Tyre
They made him a Tyre-born Greek living in Damascus, son of Naucrates; historians think this was invented to link him to the Arab world.
Q 11How many postulates does Book 1 of the Elements set out?
Five
Together with five common notions they form the axiomatic basis for everything that follows.
Q 12Which of Euclid's postulates is the famous parallel postulate?
The fifth
Attempts to prove it from the other four failed for two thousand years and eventually produced non-Euclidean geometry.
Q 13The parallel postulate says two lines meet on the side where the two interior ones sum to less than what?
Two right angles
In hyperbolic geometry infinitely many lines through a point miss a given line; in elliptic geometry every line meets it.
Q 21Book 7 of the Elements defines a "perfect number"; which is the smallest?
6
Its proper divisors 1, 2 and 3 add up to 6; the next perfect numbers are 28, 496 and 8,128.
Q 22Which of Euclid's surviving works is the earliest Greek treatise on perspective?
Optics
The Phaenomena covers spherical astronomy, and Catoptrics, on mirrors, may not be his at all.
Q 23Which lost four-book work of Euclid was superseded by a fuller treatise of the same name from Perga?
Conics
The Pseudaria warned beginners against fallacies, and the Porisms may have anticipated projective geometry.
How did ancient Greek mathematicians usually refer to Euclid?
Q 14How many definitions open Book 1 of the Elements?
20
They cover lines, angles and regular polygons; Book 1 then has 48 propositions ending with the Pythagorean theorem.
Q 15Which famous result about right-angled triangles closes Book 1, in the earliest surviving proof?
The Pythagorean theorem
Propositions 46 to 48 deliver it; medieval students nicknamed proposition 47 Dulcarnon, "the two-horned".
Q 16What is the pons asinorum, Proposition 5 of Book 1?
The isosceles triangle theorem
Latin for "bridge of asses", it was the point where weak students stumbled; another medieval name was Elefuga, "flight of the wretches".
Q 17Which book of Euclid's Elements contains the algorithm for finding a greatest common divisor?
7
It is one of the oldest algorithms still in everyday use, and works by repeatedly replacing the larger number with the difference.
Q 18What does Euclid's theorem, in Book 9, prove?
There are infinitely many prime numbers
At least 200 different proofs of it now exist.
Q 19Which numbered book of the Elements is by far the largest and deals with irrational magnitudes?
10
Book 5, the general theory of proportion, is considered among the work's most important sections.
Q 20The final book of the Elements is devoted to which five shapes?
The Platonic solids
Theaetetus described the tetrahedron, cube, octahedron, dodecahedron and icosahedron, and Euclid gave them a complete treatment.
As "the author of Elements"
The Greek is ho stoicheiotes; some medieval scholars even doubted he was a real person.
Q 25Where were the oldest physical fragments of the Elements, dating from around 100 AD, found?
A rubbish heap at Oxyrhynchus, Egypt
Papyrus Oxyrhynchus 29 preserves Book 2, Proposition 5 with its diagram.
Q 26Whose 4th-century edition of Euclid was for centuries the only surviving Greek source?
Theon of Alexandria
A manuscript not derived from Theon's was only found by François Peyrard in the Vatican in 1808.
Q 27Which English monk translated the Elements into Latin from Arabic around 1120?
Adelard of Bath
Western Europe had lost the text apart from fragments of Boethius's translation until then.
Q 28In which year did Erhard Ratdolt publish the first printed edition of the Elements?
1482
It was based on Campanus of Novara's Latin version and repeated the confusion with Euclid of Megara.
Q 29The Elements is often said to be second only to which book in number of editions published?
The Bible
The count runs well over a thousand editions since 1482.
Q 30Who published the first English edition of the Elements in 1570?
Henry Billingsley
John Dee supplied its famous "Mathematical Preface" and copious notes.