The Egyptian year was divided into twelve months of thirty days each, which means that each year was about five days short of the astronomical year. To compensate for this difference, five extra days were added to the year, called epagomenal days. Because they were not part of the normal year created by the gods, the Egyptian regarded these days as particularly ominous, and texts have survived listing exactly what may and may not be done during this period. Even the addition of these five days did not solve the concurrence problem with the solar year, however, which lasts 365 1/4 days. As a result, the calendars shifted at a rate of 1 day every four years, and over time an important gap opened up between the real and the theoretical calendars. This meant that the inundation no longer occurred in the inundation season, and the warm season no longer in the summer. The two calendars only coincided again once every 1,460 years. After an unsuccessful attempt to revise the calendar in the reign of Ptolemy III, this problem was eventually solved by the Romans by adding one leap day every four years to the Alexandrian calendar. The Greek author Plutarch has recorded his own version of the creation of the epagomenal days. The sun god Helios (the Greek equivalent of Re) had put a curse on the goddess Rhea (the Egyptian sky goddess Nut), which meant that she was unable to bear children on any of the 360 days of the year. Hermes (the Egyptian god Thoth, the god of learning) solved the problem by adding five days to the year. Five children were born on these days, Osiris, Isis, Nephthys and Seth, but also Apollo (=Horus), the latter because of the association between his original mother Hathor with the sky goddess Nut.