This is a linked open data (LOD) about date and time. "C.E. 0001 January 01" is a date of Gregorian Calendar (Calendar ID: 2.1).
http://datetime.hutime.org/calendar/2.1/date/C.E._0001_January_01
hcal:2.1/date/1721425.5
hcal:2.1/date/C.E._0001_January_01
hcaldate:1721425.5
hcaldate:C.E._0001_January_01