Artaxerxes was a Gentile King, and Nehemiah uses the fall calendar (1:1; 2:1); also the Papyrus found in Elephantine which gave evidence of a Jewish fall calendar referred to the third year of Darius II, a Gentile King.
mrasell:
You are partially right the Persians are Gentiles because they were of the Aryan ethnic tribes of people. At one time it was the Medes and the Persians but the kingdom of Mitanni was eventually taken over by the Persians. Both of these people were related but the Persian also moved into the land of Shem and took the kingdom of the Elamites and made the city Shushan their Capital.
However you are not correct about a fall calendar during the time of Nehemiah who obeyed the Commands of YAHWEH. Now after the Babylonian exile many Jews begin to adopt the pagan names of the month and later the Rabbinical school started a fall calendar claiming it to be civil usage. However, this is not true because YAHWEH Commanded on set time for the year for both civil and religious matters and that time begin in the Spring time. YAHWEH only named one month of the year as HE only named on day of the week and it was called the month of Aviv. The Jews used a lunar/solar calendar because the years would rotate back evenly after 19 cycles. The reason it this time was due to the flood and the new position the earth rotated around the sun and the moon rotating around the earth. Once the earth had 30 day each month equally but not after the flood.
This month shall be unto you the beginning of months: it shall be the first month of the year to you. Exodus 12:2
Observe the month of Abib, and keep the passover unto YAHWEH thy ELOHIM: for in the month of Abib YAHWEH thy ELOHIM brought thee forth out of Egypt by night. Deuteronomy 16:1
And it came to pass in the month Nisan, in the twentieth year of Artaxerxes the king, that wine was before him: and I took up the wine, and gave it unto the king. Now I had not been beforetime sad in his presence. Nehemiah 2:1
In the first month, that is, the month Nisan, in the twelfth year of king Ahasuerus, they cast Pur, that is, the lot, before Haman from day to day, and from month to month, to the twelfth month, that is, the month Adar. Esther 3:7
Those who were obedient kept the correct time but the Rabbinical school of thought became Hellenized and changed many of ELOHIM'S Laws.
Happy Sabbath,
stinsonmarri