Tafsiran Hakim-hakim 4:12: Metzudat David & Tze'enah Ure'enah

That he had gone up: From this he understood that he wanted to wage war; and that is why he went up, to fortify himself on the mountain.

“And Sisera was informed” [4:12]. And they told Sisera that the people had gathered on Mount Tabor. “And Sisera gathered” [4:13]. Sisera gathered all of his chariots, nine hundred chariots, and the horses had iron shoes. Our sages say that there were forty thousand chieftains and each one had one hundred thousand men. Sisera was thirty years old at the time. He was very strong and dominated the whole world. There was no city in the world that he could not make all of its walls collapse with his shout. All of the animals did not move from their cities when Sisera gave a shout because they were so afraid that they had to stay in the city since they could not run away.¹⁰Yalkut Shimoni, Judges, Remez 43.