Die Messung des Erdumfangs nach Eratosthenes
Δεῖ οὖν ἀναγκαίως καὶ τὸ ἀπο Συήνης εἰς Ἀλεξάνδρειαν διάστημα πεντηκοστὸν εἶναι μέρος τοῦ μεγίστου τῆς γῆς κύκλου · καὶ ἐστι τοῦτο σταδίων πεντακισχιλίων. ὁ ἄρα σύμπας κύκλος γίνεται μυριάδων εἴκοσι πέντε. Cleomedes, On the Circular Motions of the Celestial Bodies (de motu circulari corporum coelestium) And it is necessary that the distance between Syene and Alexandria is one-fiftieth of the Earth's circumference. Since this distance is 5000 stades the circumference length is 250000 stades.
Eratosthenes of (PDF File)
Finally there is also the posibility that he used a scaphe which is also a sun dial.
The scaphe dial, probably the oldest form of sundials. Scaphe (Greek boat) a bowl-shaped cup within which the hour-lines are marked. At the time of summer solstice the shadow is shortest and falls exactly on the bottom line. In the following time the shadow grows again until it reaches the top line at the time of winter solstice. The days are divided into temporal hours. Their length is not fixed but instead the time between sunrise and sunset is divided into 12 intervals of equal length. Klaus Kohl provides a possible method used by Eratosthenes with the scaphe to determine the circumference, avoiding the measurement of angles.
Two thousand years later, French astronomers Pierre Méchain and Jean-Baptiste Delambre set out to measure the Earth using modern methods. Their goal was to determine with precision and accuracy the distance between the Earth's north pole and its equator. By dividing that great distance into ten million equal parts, the savants, in the name of the people of France and the good of all mankind, would create a new and natural standard of measure: the meter.
According to Ptolemy Eratosthenes measured the tilt of the Earth's axis and obtained a value of 11/83 of 180 degrees.