you didn'T see tHe small text !!! REally, how could you have missEd it? that's very dishONorablE of you. SEe that next time, you do an eVEN better job.
Year 320 (CCCXX) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantinus and Constantinus (or, less frequently, year 1073 Ab urbe condita). The denomination 320 for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
taken from Wikipedia (also 221? what? you guys are getting this pretty wrong)