Alma 50:5

And they were prepared, that they could cast stones from the top thereof, according to their pleasure and their strength, and slay him which should attempt to approach near the walls of the city.

The people were ready to throw stones down from the towers. They could throw them as far as they wanted and kill anyone who tried to get close to the city walls.

From up there, they could hurl stones down with all their strength and kill anyone trying to get near the city walls.