Epagomenos

Epagomenos was the Greek name for the five days added to the cycle of 360 days to complete the solar year of 365 days.

Herodotus wrote:

The Egyptians were the first men of the world to discover the cycle of the year, dividing their duration, to conform it, in twelve parts. They claimed to have discovered it thanks to their observation of the stars.

Heroscope History II-4 (Carlos Schrader translation)

The invention of the Egyptian civil calendar arose at the beginning of the third millennium BC. C. and there is evidence of its use in the time of Shepseskaf, pharaoh of the IV dynasty of Egypt. The Egyptian civil year consisted of 365 days, divided into three seasons of 120 days, plus five added days, which did not constitute a separate month.

Those days were called by the ancient Egyptians heru renpet "those that are above the year", they were also known as mesut necheru "of the birth of the gods", since the birth of five Egyptian deities was celebrated: Osiris, Horus, Seth, Isis and Nephthys. Later, in the Coptic language, they were called piabot nkoyxi "the little month."

The first evidence of the existence of the epagomenan days comes from an inscription in the tomb of Nekanj, an official from the time of Menkaura (Old Kingdom). They are also mentioned in the Pyramid Texts.

The stations were called:

1. Flood: ajet
2. Siembra or exit: peret
3. Collection or drought: shemu

Mythology

Dyehuty (Thoth in Greek) created the five epagomenal days, removing them from the luminosity of Jonsu, lunar god. These new days allowed Nut to give birth to five children: Osiris, Haroeris or Horus the elder, Seth, Isis and Nephthys, since Ra forbade her to have them during the year.