A non-calendar year Grand Slam is equal to a calendar year Grand
If someone has held all 4 Slam titles at the same time, it doesn't
matter which Slam they began their run with! That person is a tennis
And there is nothing special about January the 1st being the
The Romans made Ianuarius the first month in 153 BC (AUC 600), when they
changed the time that the consuls were inaugurated. Years were numbered
or counted from the dates of the consuls terms. Ianuarius & Februarius
were added to the end of the existing 10-month Roman Calendar.
The first month had previously been Martius (month of Mars). Only the
first 4 months had names - Aprilis (Aphrodite), Maius (Maia) & Iunius
(Juno). The remaining months were numbered - Quintilis (5th), Sextilis,
September, October & November. Quintilis was later named after Julius
Caesare & August after Augustus. (Ianuarius was named for Juno and
Februarius from februum (a thing used for ritual purification,
reflecting its position as the last month).
It is thought that the changes in 153 BC were initiated by the 2nd King
of Rome, Numa Pompilius.
The year has been defined as starting on Jan 1st for ~2,174 years,
though some parts of the world did not follow the Roman, Julian or
It seems to me that a great deal of thought went into the changes to
the calendar we use today. Considerable changes were also established
by Julius Caesar in ~54 BC, he was advised by several astronomers such
as Sosigenes of Alexandria.