In the "Contendings of Horus and Set", the myth which tells about the fight between these two gods for the rulership of Egypt, Set injures the eyes of Horus. They are healed by Hathor who uses gazelle´s milk on them. The healed eyes became the symbol for perfection, called the 'Wedjat' or 'Udjat' Eye and are spoken of in singular.

Ref Wikipedia

The History of Ancient Egypt spans the period from the early predynastic settlements of the northern Nile Valley to the Roman conquest in 30 BC. The Pharaonic Period is dated from around 3150 BC, when Lower and Upper Egypt became a unified state, until the country fell under Greek rule in 332 BC.

Egypt's history is split into several different periods according to the dynasty of the ruling of each pharaoh. The dating of events is still a subject of research. The conservative dates are not supported by any reliable absolute date for a span of about three millennia. The following is the list according to conventional Egyptian chronology.

• Early Dynastic Period of Egypt: 31st to 27th centuries BC
• Old Kingdom of Egypt: 27th to 22nd centuries BC
• First Intermediate Period: 22nd to 21st centuries BC
• Middle Kingdom of Egypt: 21st to 17th centuries BC
• Second Intermediate Period: ca. 1640 to 1570 BC
• New Kingdom of Egypt: 1570 to 1070 BC
• Third Intermediate Period and 1070 to 664 BC
• Late Period of ancient Egypt
  • Twenty-sixth dynasty of Egypt: 664 to 525 BC
  • Achaemenid Egypt: 525 to 332 BC

• Ptolemaic Egypt: 332 to 30 BC
• Roman Egypt: 30 BC to AD 395
• Byzantine Egypt: 395 to 645

• Arab Egypt: 639 to 1250
• Mamluk Egypt: 1250 to 1517
• Ottoman Egypt: 1517 to 1805

• Egypt under the Muhammad Ali dynasty: 1805 to 1882
• Modern Egypt: since 1882