The GDate data structure represents a day between January 1, Year 1, and sometime a few thousand years in the future (right now it will go to the year 65535 or so, but g_date_set_parse() only parses up to the year 8000 or so - just count on "a few thousand"). GDate is meant to represent everyday dates, not astronomical dates or historical dates or ISO timestamps or the like. It extrapolates the current Gregorian calendar forward and backward in time; there is no attempt to change the calendar to match time periods or locations. GDate does not store time information; it represents a day.