I've done a good bit of similar code for the Tcl programming language (see http://www.tcl.tk/cgi-bin/tct/tip/173 for details). The implementation there can handle the proleptic Julian calendar, with a defined change date. There are a number of caveats worth mentioning: - Prior to the Julian conversion, different locales had different rules for when the number of the year changed. In and before 1752 in Great Britain, for instance, the number of the year changed on 25 March; 1-24 March belonged to the previous year! With the adoption of the Gregorian calendar, the change was universally 1 January. (For this reason, you'll sometimes see eighteenth-century dates as O.S. ("Old Style") or N.S. ("New Style") when the year would otherwise be ambiguous. I decided for Tcl not to bother with any kind of localized rule for year numbering in those circumstances; it was too much of a mess. - As you correctly observe, leap years were observed irregularly in Rome in Republican and early Imperial times. In fact, they were so irregularly observed that it was occasionally necessary to intercalate entire months. Again, I decided with Tcl not to bother. - It appears unnecessary to control skipping the year zero. I have not encountered any locale where there is such a beast; in all cases, it appears that the year 1 B.C.E. is followed by the year 1 C.E. - I use a message catalog (the same catalog in which I hold localised month names) to hold a locale's Julian conversion date, and then select the catalog according to LC_TIME. Tcl's ordinary message catalog functionality can be used to change the date. - I have not yet troubled to implement anything but Gregorian (or hybrid Julian-Gregorian) calendars. I did a limited amount of localization to handle the Japanese civil calendar, but only for dates after the Meiji restoration (when it's Gregorian, except that years number from the start of an emperor's reign). Incidentally, Tcl's counterpart to zic (which uses the same input format as zic) simply uses 64-bit counts of seconds for its transition times. Also, it doesn't track leap seconds, since Tcl's model of time is Markus Kuhn's "smoothed universal time" (http://www.cl.cam.ac.uk/~mgk25/uts.txt) in which leap seconds are handled by changing the length of a second by 1 part in 1000 until Tcl's clock is back in sync with UTC. -- 73 de ke9tv/2, Kevin KENNY GE Corporate Research & Development kennykb@crd.ge.com P. O. Box 8, Bldg. K-1, Rm. 5B36A Schenectady, New York 12301-0008 USA