On (also known as Heliopolis or Iono) was an ancient Egyptian city which was known as the “city of the sun” or “city of evil”. It was located in the northeastern part of the Nile Delta, near the modern city of Cairo. On was a major religious and cultural center in ancient Egypt, and was home to the famous Temple of Ra. The city was also a center of learning, and is believed to have been the site of the world’s first known university. On was a rich and influential city in ancient Egypt, and it played a significant role in the country’s history and religion.