Until early modern times the calendar in general use throughout Europe was known as the Julian Calandar, named after Julius Caesar, who introduced it in 46BC. It was based on the calculation that a year lasted 365.25 days. A ‘leap year’ was included every four years to add an extra day to February in order to correct the calendar for that additional quarter of a day.
In fact, though, the year is actually a few minutes shorter than the Julian Calendar’s 365.25 days. As a result it gained about three days every four centuries.

In 1582 Pope Gregory introduced the new ‘Gregorian Calendar. By then the Julian calendar had added ten days too many and to correct this discrepency the Pope announced that the 4 October 1582 would be followed by 15 October 1582.
In addition, Pope Gregory decreed that centenary leap years would not be leap years unless they were divisible by 400. The net result of these changes was that the discrepency would only amount to 23 seconds a year and it would take 3,700 years before it added up to an extra day. Despite the obvious advantages of the Gregorian Calendar its association with Catholicism meant it was introduced in a piecemeal fashion. Most of Catholic Europe began using it in the late sixteenth century but Russia waited until 1917 and Greece until 1923.

In Britain the Gregorian Calendar was adopted in September 1752. The discrepancy had then grown to eleven days, and to correct this error officialdom decided that 2 September 1752 would be followed by 14 September 1752.
Much as today, anything that involves change rouses British passions and there were demonstrations on the streets, demanding the return of the eleven days people believed had been robbed from them.
The date of the new year was also changed, to the first of January. Until 1751 the civil, ecclesiastical and legal new year had begun on the 25 March (Lady Day). This explains why the accounts of Gamlingay’s overseers and constables begin on 25 March and end on 24 March the following year.

What this means for researchers is that for dates between 1 January and 24 March the historical year doesn’t match the civil year. Some historians refer to dates during this period as, for example, 4 February 1656/7 (as writers such as Samuel Pepys often did at the time) but this is rather clumsy and others use the historical year, preferring in this instance to write 4 February 1657.
Confusing? You bet it is. Even something as straightforward as the entries in the parish registers have to be corrected in this way otherwise ambiguities occur.
For example, the Gamlingay parish registers registers state that Mary Luke was baptised on 12 December 1736, and buried on 13 March the same year – nine months before she was born, an obvious absurdity.
Convert to historical years and you can see that she was actually baptised on 12 December 1736 and buried on 13 March 1737.

Incidentally, if you’ve ever wondered why the new tax year starts on 6 April – an apparently arbitrary date – you can blame it on the introduction of the Gregorian Calendar. The old-style financial year started on the first day of the old new year: 25 March. Eleven days were lost in 1752, which moved the beginning of the tax year to 5 April. Another day was skipped in 1800 and pushed it back to April 6.

At first sight the names of some of the months are puzzling too. The first two syllables of September means ‘seven’, that of October ‘eight’, of November ‘nine’ and of December ‘ten’, yet these are our ninth, tenth, eleventh and twelfth months respectively.
Before 1752 it made perfect sense. The first month of the civil year was March. This made April the second month, May the third and so on. Thus September, October, November and December were the seventh, eighth, ninth and tenth months of the year.

But that’s not the end of it where dates are concerned. Most medieval documents do not refer to a day, month and year. They were dated using saints’ days and regnal years and have to be decoded in order to date them to their historical year.
Here’s a single example, using an early Merton manor court roll for Gamlingay. At the top of the roll the clerk’s heavily-abbreviated Latin records the date it was held as ‘the Wednesday next following the feast of All Saints in the 16th year of the reign of King Edward III’. Regnal years start on the day of the monarch’s accession to the throne. In Edward III’s case his 16th regnal year lasted from 25 January 1342 until 24 January 1343. All Saints’ Day falls on November 1st each year so the year in question must be 1342. The calendar for 1342 tells us that the 1st November that year fell on a Friday. The Wednesday after was therefore the 6th November. Put all that together and we’ve worked out that the court was held on Wednesday 6 November 1342.
Simples.

Jim Brown