There were twelve months, each divided into three ten-day weeks called "décades". The tenth day, "décadi", replaced Sunday as the day of rest and festivity. The five or six extra days needed to approximate the solar or tropical year were placed after the months at the end of each year and called complementary days. This arrangement was an almost exact copy of the calendar used by the Ancient Egyptians, though in their case the beginning of the year was marked by the summer solstice rather than the autumnal equinox.