Lunar calendars

I don't know if this is the right newsgroup but calendars of various
kinds are certainly part of the history of astronomy.

If you take a calendar of 12 lunar months, typically new moon to new
moon,each month is 29 or 30 days and you get a calendar of about 354
days.

Now the Moslems keep that. So about 8 years from now, Ramadam will
begin near the end of northen hemisphere Spring instead of the end of
Summer like this year..

But most calendars based on lunar months insert extra months every so
often to keep holidays in the same season. For example, the Chinese do
it by astronomical observation and the Jews have taken a formula from
Babylon in which years 3, 6, 8, 11, 14,17 and 19 of a 19-year cycle
have an extra month of Adar. (note - the first Adar is the leap month,
the second is the normal month in leap years)

So how did this system start and who started it? I believe the
pre-Moslem Arab calendar worked like this. Is there any specific
reason why the leap months were abandonned by Islam other than "this
is what Allah commanded"? Presumably it has something to do with
nomads not taking seasons as seriously as farmers.

..