# Eratosthenes Cleomedes, not a classroom globe, is the first public fact about Eratosthenes’s circumference. Britannica at https://www.britannica.com/biography/Eratosthenes and MacTutor at https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/ state that On the Measurement of the Earth is lost and that later writers preserve a Syene–Alexandria method in stadia. That is a source-limit before it is a triumph. What later reporters actually preserve is a short list. Strabo at https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.01.0198 and LacusCurtius at https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/1A*.html quote a three-book Geography and a chart of the inhabited world. ToposText at https://topostext.org/work/144 makes the same Greek-English neighbourhood searchable. Britannica’s Library of Alexandria page at https://www.britannica.com/topic/Library-of-Alexandria and the life itself print a received librarianship under Ptolemy III. Stanford’s ancient astronomy entry at https://plato.stanford.edu/entries/astronomy-cosmology-ancient/ is independent texture for the astronomical neighbourhood, not a causal dataset and not Eratosthenes’s diary. What is not a lifetime act: Nicomachus’s later arithmetic as a recovered lecture; a JavaScript sieve; a wall map in a science museum; UNESCO or tourism copy about the Pharos; Ptolemy’s second-century Geography as if it were 230 BCE; Hipparchus’s critique as if Eratosthenes wrote it. The sieve is stored as later attributed. The circumference is stored as later reported. Those labels are the point of the catalog, not a demotion of the name. Related scientific names are bounded. Archimedes corresponds with him in later mathematical tradition. Callimachus is a library predecessor. Ptolemy III is the received royal patron. Strabo is a later carrier. Hipparchus is a later critic of the geographical file. The later Claudius Ptolemy’s Almagest and Geography are a neighbouring Person catalog, not a twin of this page. Theon of Alexandria and Cleomedes are later transmitters. Euclid and Aristarchus belong to the same Alexandrian scientific city as received, not as a group photograph. A library office is not a circumference. A Geography is not a sieve. An obliquity heading is not a map. Conventional year-01-01 dates mark received floruit, not excavated daybooks. Complex contribution is required. Confidence is high that later Greek prose names these headings, medium on autograph wording, low on unique kilometre error. What the score must not say: that he authored [Ptolemy](/people/ptolemy); that a school experiment is 240 BCE; that Catasterisms is an undoubted autograph stored here; that a missing Mouseion payroll can be filled by invention. Remaining dated instruments kept after dropping later editions, museums, and split rows: -0245-01-01 Eratosthenes is appointed to the Alexandrian library under Ptolemy III as later lives report; -0240-01-01 A measurement of Earth’s circumference is later reported under Eratosthenes’s name, principally by Cleomedes; -0230-01-01 A three-book Geography under Eratosthenes’s name is later quoted by Strabo as a completed treatise; -0235-01-01 A prime-number sieve is later attributed to Eratosthenes; it is not a recovered classroom autograph; -0220-01-01 Chronological tables under Eratosthenes’s name later attempt to fix literary and political dates from Troy onward; -0240-06-01 A measurement of the ecliptic’s obliquity is later credited to Eratosthenes as a distinct astronomical heading; -0230-06-01 A map of the inhabited world with measured intervals is later described as Eratosthenes’s cartographic scheme. Later Loeb, UNESCO, and encyclopedia pages are evidence, not additional acts. ### Coordinates, measurement, and the missing original The chief weakness in the evidence for Eratosthenes is the disappearance of his geographical treatise, not a shortage of modern diagrams. A measurement repeated by Cleomedes cannot be inspected in Eratosthenes' own notebook. Even the familiar story of parallel solar rays at Syene and Alexandria involves reported assumptions: city separation, local solar position, observational timing, and a model of a spherical Earth. The calculation can be reconstructed mathematically; the exact field procedure cannot be recovered from an eyewitness log. Treating each modern reconstruction as an additional scientific action would multiply a single, incompletely transmitted achievement into fictional events. D. Graham J. Shipley's 2024 study draws attention to a more substantial geographical legacy. It presents 127 translated extracts and argues that an exclusive fixation on the circumference obscures Eratosthenes' work on latitude, longitude, and topographical divisions of the inhabited world. That is a different intellectual accomplishment from estimating the planet's size. A coordinate-based account organizes distances and regions so that knowledge can be compared, corrected, and transmitted. Reports by Strabo remain crucial carriers, but Strabo's disagreements and editorial choices are part of the evidence. Neither Strabo's survival nor a modern reconstruction supplies a contemporary map in Eratosthenes' handwriting. The Alexandria library context also requires careful attribution. The institutional availability of texts, instruments, scholars, and royal patronage made sustained comparison possible. It does not establish that the librarian personally authored every later practice assigned to the Alexandrian school. The traditional prime-number sieve and calculations of axial tilt must be distinguished from work securely described in the ancient transmission; later mathematical nomenclature is not itself proof of authorship. Conversely, uncertainty about attribution does not erase the methodological significance of the received geographical fragments. A defensible assessment identifies the claimed method, the intermediate transmitter, and the point at which a conjecture becomes modern extrapolation. The relevant intellectual line leads forward to Ptolemy, whose Geography developed a different geographical system many generations later. It is a history of inheritance and correction, not evidence of collaboration between contemporaries. The broader [education and access to knowledge](/drivers/edu-digital-learning-access) connection concerns the durability of educational access to mathematical procedures and geographical arguments. That is an interpretive domain connection rather than a fabricated measurement of social benefit in Ptolemaic Egypt. The responsible record can be rich while retaining a sharp boundary between ancient acts, later witnesses, and present-day teaching. ## Dated facts - 244: Eratosthenes is appointed to the Alexandrian library under Ptolemy III as later lives report. https://factrail.ai/facts/era-library-appointment. Sources: https://www.britannica.com/biography/Eratosthenes, https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/. - 240: A measurement of the ecliptic’s obliquity is later credited to Eratosthenes as a distinct astronomical heading. https://factrail.ai/facts/era-obliquity-ecliptic. Sources: https://www.britannica.com/biography/Eratosthenes, https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/. - 240: A measurement of Earth’s circumference is later reported under Eratosthenes’s name, principally by Cleomedes. https://factrail.ai/facts/era-circumference-cleomedes. Sources: https://www.britannica.com/biography/Eratosthenes, https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/. - 235: A prime-number sieve is later attributed to Eratosthenes; it is not a recovered classroom autograph. https://factrail.ai/facts/era-sieve-later-attributed. Sources: https://www.britannica.com/biography/Eratosthenes, https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/. - 230: A map of the inhabited world with measured intervals is later described as Eratosthenes’s cartographic scheme. https://factrail.ai/facts/era-oikoumene-map. Sources: https://topostext.org/work/144, https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.01.0198. - 230: A three-book Geography under Eratosthenes’s name is later quoted by Strabo as a completed treatise. https://factrail.ai/facts/era-geography-three-books. Sources: https://www.britannica.com/biography/Eratosthenes, https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.01.0198. - 220: Chronological tables under Eratosthenes’s name later attempt to fix literary and political dates from Troy onward. https://factrail.ai/facts/era-chronographiai. Sources: https://www.britannica.com/biography/Eratosthenes, https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/. ## Methodology https://factrail.ai/methodology Canonical: https://factrail.ai/people/eratosthenes