Acoreus was the name of a wise man consulted by Julius Caesar, according to the Roman writer Lucan, asking him many questions about Egypt’s history and its calendar. Caesar learned that the Egyptians based their year by the solar year, that is, one revolution of the earth around the sun) measuring this by the rise of the brightest star in the Eastern sky, Sirius, and the flooding of the Nile.
The Egyptians were the first people to base their calendar, like our modern version, on the solar year. Although without sophisticated technology to arrive at their conclusions, their calendar remarkably also consisted of 365 days. These consisted of 12 months of 30 days each with five extra days added at the end of the year to make up the difference. These ingenious ancient people even introduced a leap year system similar to ours. In about 238 BC King Ptolemy III added an extra day to every fourth year.
After he had learned about the Egyptian calendar, Caesar was determined to reform the Roman system. The Romans used a calendar based on the 12 month lunar year which is. based on the phases of the moon, plus extra days and months inserted to keep it in line with the seasons.
(at least the part below this)
By 46 BC this system was being abused. The priests failed to insert extra months and intentionally manipulated it for political reasons - to prolong the official’s terms of office or hasten or delay elections.
In 46 BC Caesar decreed that the Roman calendar be reordered, appointing the Alexandrian astronomer Sosigenes to do the calculations. Sosigenes replaced the Roman lunar system of 355 days per year with a solar year of 365 days. A leap year was added by the addition of an extra day to every fourth February. This so-called Julian calendar also established the days of the week, as we know them, although with different names.
