The Earth's circumference was first calculated in 240 BC by Eratosthenes using the angle of the Sun during the solstice in 2 cities 500 miles apart (the measurement took 1 year: he walked from Aswan to Alexandria to take the measurement there at the following solstice).
He theorized that the Earth was a sphere, and his calculation was within 5% of modern measurements.
the china my grandparents bought (in Germany, during the reconstruction) I've eaten on every Thanksgiving for half a century, is now mine to care for, lots of memories