Judges 4:13

‘ And Sisera gathered together all his chariots, even nine hundred chariots of iron, and all the people who were with him from Harosheth of the Nations, to the river Kishon.'

Sisera was taking no chances, and this was to be a massive show of strength to prevent such incidents happening again. He called together his chariot force of nine units of chariots, and his soldiers and mercenaries who dwelt in Harosheth of the Nations, probably a garrison town. These were the forces immediately available. Then he amassed them in the plain beside the river Kishon. This was within easy reach of Mount Tabor.