# A measurement of Earth’s circumference is later reported under Eratosthenes’s name, principally by Cleomedes Date: 240 ## The fact Britannica and MacTutor print that [Eratosthenes](/people/eratosthenes) measured Earth’s circumference from the difference of noon shadows at Syene and Alexandria, obtaining a figure in stadia. The surviving public method is later: Cleomedes’s astronomical lectures, not an autograph On the Measurement of the Earth. It is one event. ## Context Strabo and Theon of Smyrna also carry numbers. The length of the stadion is disputed; this catalog does not supply a unique kilometre error bar. Parallel-ray geometry as later taught is a method path of high confidence on the later report, medium on the lost treatise’s wording. Eratosthenes’s documented role is bounded by other offices and collaborators named in the sources below. Sharing a field with them is not a reason to drop a documented act, and it is not a reason to assign later consequences done in the name after death. Conventional years are c.276–c.194 BCE. Almost no autograph survives. Cleomedes, Strabo, Nicomachus, and later encyclopedias are the public file. Classroom globe reconstructions are not his acts. Contribution is complex. Named person as heading of the dated public instrument. Later editors, museums, printers, or offices share publication. Complex where later carriers are the surviving public file. ## Evidence and sources Britannica’s biography and MacTutor independently describe the Syene–Alexandria method as later reported. Cleomedes is named in both as a principal later carrier. Official or archival record: MacTutor — Eratosthenes of Cyrene (https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/; University of St Andrews). ## Significance A later-reported geodetic method is a knowledge-access path. It is not a GPS series and not a permission to invent a 240 BCE field notebook. ## What is established and what is not Established: later Greek scientific prose attributes a stadia circumference to him. Not established: the autograph treatise, the exact stadion, or that a modern school experiment is his act. What would change the picture: a contradictory original with a different date or name, or a measured series that can be argued, with lag and alternatives, as a consequence of this instrument rather than of later institutions. The date is the date of this instrument, not a licence to back-date every later harm or benefit. Established here: a sourced, dated public instrument with a named contribution by Eratosthenes. They are not a public rating. Eratosthenes did not file a later UNESCO form, a later Loeb colophon, or a later museum label as a personal act. A portrait or conventional bust is not this mechanism. Allegation, reconstruction, and established occurrence stay distinct. Keep Cleomedes’s date as the reporter, not as Eratosthenes’s death year. Keep the carrier date of later English distinct from the received historical year stored in the date field. Do not read a later English edition as a recovered autograph of Eratosthenes. ## People - Eratosthenes: https://factrail.ai/people/eratosthenes ## Drivers - Digital Learning Access: https://factrail.ai/drivers/edu-digital-learning-access ## Sources - https://www.britannica.com/biography/Eratosthenes - https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/ ## Methodology https://factrail.ai/methodology Canonical: https://factrail.ai/facts/era-circumference-cleomedes