Really you guys? Think about where he lived, Alexandria which was further north than Syene. In Alexandria during the summer solstice the sun was never directly overhead while in Syene the sun was directly overhead. He simply measured the shadows a year apart on the summer solstice, same time of day, different shadow lengths. He could simply have arranged for a colleague to take the measurement on the same summer solstice and the data could be collected after a few days travel between Syene and Alexandria.
Really you guys? Think about where he lived, Alexandria which was further north than Syene. In Alexandria during the summer solstice the sun was never directly overhead while in Syene the sun was directly overhead. He simply measured the shadows a year apart on the summer solstice, same time of day, different shadow lengths. He could simply have arranged for a colleague to take the measurement on the same summer solstice and the data could be collected after a few days travel between Syene and Alexandria.