We know almost nothing about Thales of Miletus. Later generations told many anecdotes about this wise man, but it is difficult to verify the reliability of these stories. What seems certain is that he predicted the solar eclipse of 28 May 585, which was remembered because the Lydian king Alyattes and the Median leader Cyaxares were fighting a battle on that day. Another reliable bit of information is that he did some geometrical research, which enabled him to measure the pyramids. However, his most important contribution to physics and philosophy is his attempt to give non-religious, rational explanations for physical phenomena. Behind the phenomena was not a catalogue of deities, but one single, original principle. Although his hypothesis that this principle was water is rather unfortunate, his idea to look for deeper causes was the true beginning of philosophy and science.
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Democritus of Abdera proposed that matter was made up from atoms. There was no real evidence for this idea (which was not completely new), but is explained why change was possible. The atoms were always moving and clustering in various, temporary combinations. Therefore, things seemed to change, but 'not being' never changed into 'being'. (It was assumed that 'not being' was a vacuum, which means that it is in fact not a 'not being' because a vacuum exists in at least four dimensions.) The consequence of this idea is that we are allowed to use our senses, although Democritus warns us to be careful.
Musei Capitolini, Roma
Hardly anything is known about Hippocrates of Cos, except for the fact that his reputation as the greatest physician of all times had already been firmly established in the fourth century. It is likely that he was born in 460, but the year of his death is a mystery, although 377 has been mentioned. Not even his own writings can be used to gain knowledge about the man, because the Corpus Hippocraticum was collected in the second century, and contains spurious material. However, it is certain that Hippocrates made medicine an independent discipline and did much for its professionalisation. One of his principles was that one could not study an illness in isolation, but had to study the patient as a whole. For several diseases, he discovered the cause in a wrong way of life.
Kérylos Villa, Beaulieu
The most famous student of the Athenian philosopher Plato was the Macedonian scientist Aristotle of Stagira (384-322). After the death of his master, he studied biology and accepted a position as teacher of the Macedonian crown prince Alexander. When the Macedonians subdued Greece, Aristotle founded a school at Athens. Most of his writings are lost; what remains are his lecture notes, which were rediscovered in the first century BCE. During the last decades, scholars have started to re-examine the fragments of the lost works, which has led to important changes in our understanding of Aristotle's philosophy. However, the accepted view remains that he replaced his master's speculations with a more down-to-earth philosophy. His main works are the Prior Analytics (in which he described the rules of logic), the Physics, the Animal History, the Rhetorics, the Poetics, the Metaphysics, the Nicomachean Ethics, and the Politics. All these books have become classics, and it is not exaggerated to say that Aristotle is the most influential philosopher of all ages and the founder of modern science.
Archaeological museum, Palermo
The great mathematician Euclid is said to have lived c.300 BCE and was connected to the Museum at Alexandria, a scientific institute created by king Ptolemy I Soter. In the thirteen books of the Elements, Euclid summarized and systematized all mathematic knowledge of his age. He also published works on optics and the theory of music. However, he is best known as a mathematicst. No work of ancient art approaches the pure and surprising beauty of Euclid's proof that there are infinitely many prime numbers.
Aristarchus of Samos (c.310-c.230 BCE) was the first to catch a glimpse of the immense size of the universe. Until then, everyone had believed that the moon, sun, planets, and stars all revolved around the earth. Perhaps the stars were as far away as twenty of forty radiuses of the earth, perhaps hunderd or thousand (the maximum size according to Archimedes), but nobody thought that it would be much bigger. But Aristarchus argued that the sun was about nineteen times the size and distance of the moon. The consequence of his calculation was that the sun was larger than the earth, and this in turn led to the conclusion that it was possible that it was not the sun, but the earth that was moving. Although several ancient astronomers, a.o. Seleucus of Babylon, subscribed to this correct interpretation of the phenomena, it was ignored until Copernicus. The correctness was not proven until Bessel in 1839 measured the parallax.
One of the most original thinkers of Antiquity was Archimedes of Syracuse (287-212). Because our approach to physics is based upon a model that was developed by this scientist, we immediately recognize him as 'one of us'. And indeed: he did all kinds of experiments and brought the results together in a law of physics - the famous Law of Archimedes. He was also interested in mathematics, which led to a new approximation of pi and a remarkable treatise, The sand-reckoner, in which he showed that he could command really big numbers by calculating the number of grains of sand in the universe. Archimedes was also interested in engineering and invented a hydraulic organ and a planetarium (which implies that he thought that the motions of heaven could be described as if they were mechanical). The invention of a machine to lever ships from a dock to the sea made him boast that if he only had a point to stand on, he would move the earth. When Roman general Marcellus besieged Syracuse, Archimedes invented war machines. During the sack of the city, he was killed (text).
One of the students of the great poet Callimachus of Cyrene was Eratosthenes of Cyrene (c.275-192 BCE), who became librarian in the Museum, the scientific institute of Alexandria. He invented a new method to calculate prime numbers, drew a famous world map, catalogued several hundreds of stars, but became especially famous for his calculation of the circumference of the earth, based on the angle of the shadow that the sun made over a vertical pole at Alexandria at noon and the fact that at the same time, the sun light fell straight into a well as Syene in southern Egypt. He concluded that the circumference was 45,460 kilometers, which is pretty close to the real figure. He also wrote a treatise on chronology and a book on musical theory, composed poems and comedies, and was responsible for two dictionaries and a book on grammar. As an ethnologist, he suggested that the common division between civilized people and barbarians was invalid (text). Eratosthenes was nicknamed bêta or 'number two', because in no branch of science he was ever the best, although he excelled in nearly every one of them.
The stellar catalogue made by Hipparchus of Nicaea contains observations that can be dated to 162-128 BCE, and this gives us an indication about the period in which he lived. Unfortunately, this is about everything we know about this astronomer, who was the first to discover the precession, i.e. the slow reorientation of the earth's axis. He was able to do this because he possessed the sky map of Eratosthenes and age-old Babylonian observations and knew the theories of the great Kidinnu. Unfortunately, Hipparchus ignored Kidinnu's calculation of the length of the solar year. The Greek astronomer's estimate had an error of 6½ minutes, whereas the Babylonian was only 4½ short of the real length of the year. Nevertheless, Hipparchus was able to improve the calendar. Another triumph was the accurate calculation of the distance to the moon, and the improvement of the world map of Eratosthenes.
Strabo of Amasia (c.62 BCE - c.24 CE) is the author of one of the largest works of geography from Antiquity. His mother's family had been important during the reign of king Mithridates VI of Pontus, but during the war against the Roman general Pompey, it had switched sides. This loyalty provided Strabo with connections in the Roman world. The seventeen books of his Geography are partially based upon autopsy (Asia Minor, Greece, Italy, Egypt), and partially on good sources like Polybius of Megalopolis and Megasthenes (who had visited India). The books are written in a simple Greek, but are more entertaining than other ancient works of geography.
Like Aristarchus, Eratosthenes, and Hipparchus, Ptolemy of Alexandria (c.85-c.165) was interested in both geography and astronomy. On both subjects, he published important works. His astronomical book was called the Megalê Syntaxis, the 'big explanation'. It is a summary of all astronomical knowledge of his age, and it remained the most important work on this subject until the sixteenth century, especially because he gave mathematical explanations of the phenomena. After Antiquity, the Arabs translated it and called it Almagest, under which name it is still known. In his Tetrabiblos, Ptolemy explained the importance of astrology, and told how the stars influenced countries and individuals. In the eight books of his Geography, he deals with map making and describes the entire known earth. It remained one of the most important works until 1488, when Bartolomeus Diaz reached the Cape of Good Hope and proved that Ptolemy's statement that one could not circumnavigate Africa was simply wrong. Double portrait of Ptolemy in a medieval manuscript from Bruges
Galen of Pergamon (129-216) started his career as physician of gladiators, but he became court physician of the Roman emperors Marcus Aurelius, Commodus, and Septimius Severus. He published many books, which he had to rewrite after his library was destroyed by fire in 191. These book became extremely influential in the Middle Ages, when they were well-read in both the Byzantine empire and the Arab world. Great scientists like Ibn Sina, Ibn Rushd and Vesalius based their researches on the foundations laid by Galen. Being both a doctor and a writer, he was rather indiscreet, but on the other hand: we now have the entire medical status of two emperors.
