‘ And so it was that when they brought out these kings to Joshua, Joshua called for all the men of Israel and said to the chiefs of the men of war who went with him, “Come near. Put your feet on the necks of these kings.” And they came near, and put their feet on their necks.'
What Joshua now did was in order to give strength and encouragement to his commanders, and to their battalions. He wanted them all to feel involved. It would sustain the battalions in future battles to remember how their chiefs had been able to demonstrate their authority over these kings.
The putting of the feet on the neck was a symbolic action demonstrating overlordship. It is well witnessed on Assyrian and Egyptian representations. Compare 1 Kings 5:3; Psalms 110:1; Isaiah 51:23.