It's fairly obvious, the monuments such as the Pyramids, the Sphinx, the many ancient temples, albeit in ruins but still there. All of this would be meaningless had the "Rosetta Stone" not be discovered. The Stone had an edict written in ancient Hieroglyphs with a translation written in Greek. Jean Francois Champollion was able to decipher the Hieroglyphs using the Greek text & now we know how to read ancient Egyptian writings.
Edit: Not many people know this but the ancient Egyptians had a 365 day calender that the Romans borrowed & it eventually "evolved" to become the standard calender we use today.
Edit: Not many people know this but the ancient Egyptians had a 365 day calender that the Romans borrowed & it eventually "evolved" to become the standard calender we use today.