Eratosthenes of Cyrene

Greek scholar and inventor

• Born: c. 285 b.c.e.
• Birthplace: Cyrene, Cyrenaica (now in Libya)
• Died: c. 205 b.c.e.
• Place of death: Alexandria, Egypt

Through his energetic directorship, Eratosthenes helped make the Library of Alexandria the greatest repository of learning in the Mediterranean world, and his varied contributions made him the most versatile scholar and scientist of the third century b.c.e.

Early Life

Eratosthenes (ehr-ah-TAWS-theh-neez) was born in the Greek North African city of Cyrene about 285 b.c.e. The only surviving ancient biographical reference places his birth in the 126th Olympiad (276-273 b.c.e.), but this is too late to allow his reported meeting in Athens with Zeno of Citium, founder of Stoicism, who died around 261. His subsequent career suggests, moreover, that he was about forty years of age when he was called to Alexandria in 245; a birth date in the mid-280’s therefore seems accurate. Because neither his name nor that of his father, Aglaus, is otherwise mentioned in Cyrenaean records, it seems that Eratosthenes was not of an especially prominent family.

While his family was not illustrious, his mother city had achieved considerable renown. Founded by Greeks from Thera before 600, Cyrene had prospered as an independent city-state. Following the death of Alexander the Great in 323, however, the Hellenistic Age brought a new political order in which large, bureaucratic monarchies dominated and absorbed the formerly autonomous city-states. Cyrene grudgingly accepted incorporation into the neighboring Ptolemaic kingdom of Egypt, which was ruled from Alexandria.

Founded by Alexander in 331, by Eratosthenes’ time this harbor city was well on the way to becoming the commercial and cultural center of the Mediterranean world. Thanks to the generous subsidies of the Ptolemies, the city boasted the great Library and its adjunct Museum, a school of advanced studies that attracted scholars in literary and scientific studies, including Callimachus of Cyrene.

The most famous poet of the early third century and compiler of the Library’s first catalog, Callimachus was the latest in a long line of Cyrenaean intellectual figures. Eratosthenes thus followed in a well-established tradition of Cyrenaean learning and scholarship when he undertook his early training at home with the renowned grammarian Lysanias. One might have expected him to pursue advanced studies in nearby Alexandria in the company of his countryman Callimachus, but the young man was primarily interested in philosophy, and for philosophy one went to the city of Socrates and Plato. Therefore, at age fifteen, Eratosthenes sailed to Athens, where he would remain for twenty-five years.

Life’s Work

Eratosthenes later recalled that in Athens he found more philosophers than had ever been known to exist within the walls of one city. The eager student sampled all of their offerings and came away disappointed. He studied Stoicism with the aged Zeno, founder of the school, but he spent more time with Zeno’s revisionist pupil, Ariston of Chios, who became the subject of one of Eratosthenes’ earliest works, a biographical sketch titled Ariston. He also witnessed the flamboyant diatribes of Bion of Borysthenes, the son of a former slave and a prostitute, who preached the doctrines of Cynicism on street corners and dockside. Eratosthenes accused Ariston of not living true to his Stoic principles and Bion of adorning his philosophy to attract more attention, much like a tart in gaudy clothes.

Eratosthenes seems to have been more receptive to the Platonism that he learned from Arcesilaus, head of the Academy in this, its “middle” period. His first seriously intellectual work, the Platonikos (platonics), followed the dialogue format pioneered by Plato and explored traditional Platonic cosmological and mathematical themes. He also wrote another philosophical study titled Peri agathon kai kakon (on good and evil qualities), which has been lost. Eratosthenes’ eclectic approach to his philosophical studies together with his criticisms of established philosophers provoked some later scholars to accuse him of dilettantism.

Less than satisfied with his experiences in philosophy, Eratosthenes fared somewhat better with poetry, the field in which he first achieved a degree of recognition. Although none of his early poetic pieces survives, two poems are known by name. The hexameter Hermes (c. 250) recalled the birth and career of that god, while the Erigone employed elegiac verse to portray the legendary suicide of an Athenian maiden. Both displayed the highly polished style of Callimachus, and the latter poem was later described as completely faultless. Without a doubt it was his early reputation as a poet, not his work in philosophy, that brought Eratosthenes’ name to the attention of the royal patrons in Alexandria when the poet Apollonius of Rhodes retired from his position as librarian in 245.

Ptolemy III Euergetes must have considered other, equally famous poets for the position of librarian, but personal and political factors led him to invite Eratosthenes to Alexandria. While Eratosthenes had pursued his studies in Athens, his homeland had enjoyed a period of independence under the rule of Magas, a renegade Ptolemaic governor who had broken with the government in Alexandria and for several decades styled himself king of Cyrene. In 245 Cyrene had only recently returned to Ptolemaic rule, largely as a result of the conciliatory marriage of Ptolemy III to Berenice, the daughter of Magas. Less than a year on the throne, the young king sought a further gesture of reconciliation to Cyrenaean opinion. Many Cyrenaeans enjoyed Ptolemaic patronage in Alexandria, but none of them, not even the great Callimachus, had been offered the prestigious post of librarian. In addition, the aging Callimachus no doubt lobbied the king on behalf of his countryman Eratosthenes. Consequently, the invitation arrived in Athens, probably in 245, and Eratosthenes sailed for Alexandria to begin the greatest phase of his life.

In assuming the title of director of the Library, Eratosthenes accepted a post of huge prestige, one that brought great responsibilities as well as opportunity. In addition to serving as tutor to the royal children, he admirably fulfilled his primary obligation to maintain and develop the largest repository of learning in the world.

During his tenure, the Library acquired authentic texts of the great tragic dramas of Aeschylus, Sophocles, and Euripides and opened an entire section dedicated solely to the study of Homer. As competition for manuscripts developed with the founding of a rival institution at Pergamum, it may have been at Eratosthenes’ behest that the Alexandrian harbor authorities began requiring all ships to surrender their books for inspection and possible duplication.

Despite his archival and tutorial duties, Eratosthenes found time to take advantage of the scholarly opportunities offered by his position—full access to the immense holdings of the Library and to the circle of resident scholars at the nearby Museum.

Because he refused to specialize and instead explored almost every area of learning, his admirers gave him the nickname “Pentathlos,” for the all-around athletes of the Olympic pentathlon. His critics preferred to call him “Beta,” that is, second-best in many endeavors but never first. That he abandoned his original interest in philosophy in favor of other fields is understandable, for the intrigue-ridden court of an authoritarian monarch was not the place to pursue moral and constitutional questions. Although none of his works survives intact, it is possible to reconstruct the main lines of his achievement.

Eratosthenes’ three-volume Geographika (geography) drew on the work of earlier geographers, but in two ways it represented a more scientific and systematic approach to the subject. He completely rejected the commonly accepted notion that writings such as Homer’s Odyssey (c. 725 b.c.e.; English translation, 1614) contained reliable geographic information. He angered many established geographical authorities when he declared, “You will find the scene of the wanderings of Odysseus when you find the cobbler who sewed up the bag of the winds.” Nor was Eratosthenes content merely to describe geographical phenomena and assign them to the various continents. Instead, by establishing distances and positions in relation to two primary axes intersecting at Rhodes, he created the first reasonably accurate map of the world. Admittedly crude, Eratosthenes’ map anticipated the modern system of longitude and latitude, and it was the first to incorporate the knowledge of Eastern regions derived from Alexander the Great’s expedition.

Eratosthenes’ Peri tes avametreoeos tes ges (on the measurement of the earth) presented his most famous geographical achievement—a calculation of Earth’s circumference. By means of a novel and elegantly simple application of two of Euclid’s geometric propositions, Eratosthenes reasoned that the distance from Alexandria to Syene in Upper Egypt represented one-fiftieth of Earth’s circumference. Coupling this figure with the known distance between the two cities, a measurement perhaps obtained at his request by Ptolemy’s royal surveyors, Eratosthenes arrived at his figure of 252,000 stades (24,662 miles or 39,777 kilometers). Far more accurate than the then generally accepted estimate of 300,000 stades, Eratosthenes’ result falls within 1 percent of the best modern measurements.

As he attempted to systematize geography, Eratosthenes also sought to replace the myriad local chronographical schemes with a universal chronology for all Greek history. A preliminary study, the Olympionikai, prepared an authoritative list of Olympic victors that could serve as a chronological yardstick. In his Chronographiai (chronological tables), which covered the period from the Trojan War to the death of Alexander, Eratosthenes placed events from various local and regional traditions in one coherent chronological system based on Olympiads.

In the field of mathematics, Eratosthenes is best known for his “sieve”—a method for discovering prime numbers—and for his solution to the “Delian Problem,” the long-standing problem of doubling a cube. For the latter, Eratosthenes composed a proof and designed a mechanical instrument, his “mesolabe,” to demonstrate it. In Alexandria he dedicated a monument bearing a model of the instrument, the proof, and his poem in praise of his patron, Ptolemy III. His longest mathematical treatise, On Means, of undetermined content, formed part of the Royal Mathematical Collection. Although Eratosthenes’ mathematical work did not match his outstanding achievements in geography and chronography, it is worth noting that the greatest mathematician of his day, Archimedes, valued his opinion and corresponded with him on mathematical issues.

The most important of his works on literary subjects was the Peri archaias komoidias (on ancient comedy), in at least twelve books, which dealt with the foremost authors of that genre—Aristophanes, Cratinus, Eupolis, and Pherecrates. The few surviving fragments indicate that Eratosthenes was concerned with variations in the dialect and vocabulary of the plays as well as the history of their revisions and stagings.

A fragment of Eratosthenes’ last work, the Arsinoe (biography of Arsinoe III), reveals the aging scholar’s sympathy for the wife and sister of Ptolemy IV. Eratosthenes recalls that while walking with him at the palace during the rowdy “Feast of the Beakers,” the queen shared with him her disgust over her husband’s drunken celebrations. Shortly after the murder of this hapless queen in 205, Eratosthenes, at age eighty, met his own death, reportedly by voluntary starvation after he had gone blind. He was buried at Alexandria within sight of the Library.

Significance

In his career, Eratosthenes perfectly exemplifies the apolitical cosmopolitan culture of the Hellenistic period. Uninterested in the political affairs of his city-state, he abandoned Cyrene for the cultural attractions of Athens, just as he later accepted the patronage of the Ptolemies. His work as librarian helped make Alexandria the outstanding center of learning in the Mediterranean world. Sadly, his remarkable scholarship had limited influence on later generations, and his reputation faltered. This circumstance is explained by his failure to produce students and by the envy that his exceptional versatility engendered. The outstanding geographer and chronographer of his day, Eratosthenes also applied his powerful and independent intellect to important questions of mathematics and to literary studies. A polymath of extraordinary abilities, he definitely was no dilettante. Perhaps Eratosthenes is best recalled by the name that he coined to describe himself—philologos, a lover of human reason in all its various forms.

Bibliography

Cunningham, Clifford J. “Updating Eratosthenes.” Mercury 32, no. 2 (March/April, 2003): 10. Discussion of the measurement of the planet Earth.

Fraser, P. M. “Eratosthenes of Cyrene.” Proceedings of the British Academy 56 (1970): 175-207. This article attempts to resolve the considerable chronological and source problems associated with Eratosthenes’ life. An excellent single work on Eratosthenes’ career.

Fraser, P. M. Ptolemaic Alexandria. 3 vols. Oxford, England: Clarendon Press, 1972. This monumental work provides a detailed view of Alexandrian society, politics, and intellectual life. It is especially good on the history of the Library and the Museum. Most valuable are its sensible reconstructions based on the fragments of Eratosthenes’ lost works.

Grafton, Anthony. “Dating History: The Renaissance and the Reformation of Chronology.” Daedalus 132, no. 2 (Spring, 2003): 74-85. Covers Eratosthenes in discussion of geography and chronology in the ancient world.

Heath, Thomas L. A Manual of Greek Mathematics. Reprint. New York: Dover, 1963. This volume places Eratosthenes in the context of the overall development of Greek mathematics, especially in chapters 7 and 11.

Lloyd, G. E. R. Greek Science After Aristotle. New York: W. W. Norton, 1973. Provides an excellent overview of Greek science in Eratosthenes’ time but has only a brief reference to him in chapter 4. Includes a diagram of his measurement of the earth.

Pfeiffer, Rudolf. History of Classical Scholarship: From the Beginnings to the End of the Hellenistic Age. Oxford, England: Clarendon Press, 1976. This standard study of Greek scholarship in the classical and Hellenistic periods has an excellent chapter that briefly discusses the chronological problems associated with Eratosthenes’ life and provides a complete catalog of the works attributed to him.

Tarn, W. W., and G. T. Griffith. Hellenistic Civilisation. 3d ed. London: Methuen, 1966. This classic study provides an overview of Eratosthenes’ world, most notably in the chapters on Ptolemaic Egypt and Hellenistic intellectual life.

Thomson, James Oliver. History of Ancient Geography. New York: Cambridge University Press, 1965. Provides an overview of the evolution of geographical knowledge and theory from early Babylonia to the later Roman period. See chapter 4 for a discussion of Eratosthenes. Includes two excellent maps based on his theories.