In ancient Egypt, the civil year was a quarter of a day too short in relation to the rising of Sothis (Sirius), the Dog star, so that the new year advanced by one day every four years; New Year's Day and the rising of Sothis coincided again only after approximately 1,460 years. Period elapsing between each such rising is known as Sothic cycle. The error with respect to the 365-day year and the heliacal risings of Sirius amounted to one day every four tropical years, or one whole Egyptian calendar year every 1,460 tropical years (4 365), which was equivalent to 1,461 Egyptian calendar years. After this period the heliacal rising and setting of Sothis would again coincide with the calendar dates. The dates for the start of each Sothic cycle are fortunately known because the Roman historian Censorinus fixed the coincidence of New Year's Day and heliacal rising of Sothis in 139 AD. Taking into account a slight difference between a Sothic year and a year of the fixed stars, the years 1322, 2782, and 4242 BC are taken as starting points of a Sothic cycle. Sothis appeared immediately preceded the Nile flood and was important in the Egyptian calendar; the cycle is strictly not of Sothis, which did not vary, but of the civil calendar.