 According to the later writers Censorinus and Macrobius, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, alternately 377 and 378 days long.In this system, the average Roman year would have had days over four years, giving it an average drift of one day per year relative to any solstice or equinox.Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days (thus 11 intercalary years out of 24).