One related fact that I’ve always found to be interesting.... Because of the ‘drift’ in the Julian calendar over the years, 10 days were removed from the Gregorian calendar when it was introduced in 1582. What this meant was that Oct. 4, 1582 was the last day of the Julian calendar and the next day was October 15, 1582 in the Gregorian calendar. This change corrected the ‘drift’ that had happened over the years and the date shift meant that vernal equinox once again happened on March 21. Why was March 21 selected you may ask? Well, the Catholic church had a lot to do with the entire makeup of the calendar and March 21 was the date of the First Council of Nicaea in 325 AD.
Also for the record, the Gregorian calendar also has some drift to it... but that is only about one day every 3,030 years.
The calendar adjustment happened at various times in different countries, which must have been a little nuts. In the British dominion the adjustment was made in the mid-18th century.
https://www.linkedin.com/pulse/mystery-behind-january-1st-1753-syed-imad-husain
https://www.timeanddate.com/calendar/monthly.html?country=9&month=9&year=1752