10 They assembled at Jerusalem in the third month of the fifteenth year of Asa’s reign.

Read 2 Chronicles 15:10 Using Other Translations

So they gathered themselves together at Jerusalem in the third month, in the fifteenth year of the reign of Asa.
They were gathered at Jerusalem in the third month of the fifteenth year of the reign of Asa.
The people gathered at Jerusalem in late spring, during the fifteenth year of Asa’s reign.