Alma 49:19

And thus were the Nephites prepared to destroy all such as should attempt to climb up to enter the fort, by any other way, by casting over stones and arrows at them.

So the Nephites were ready to destroy anyone who tried to climb up and enter the fort any other way. They would throw stones and arrows at them.

The Nephites were ready to destroy anyone who tried to climb the walls by raining down stones and arrows.