Legge's translation of the sixth and topmost line describes the city wall falling back into the moat from which the earth to build it was originally taken, and states plainly that it is not the time to use the army, though one may still announce one's orders within one's own city, and that even firm correctness here brings occasion for regret. Where the earlier lines built and maintained a genuine peace, this final line watches that structure return to the raw ground it was raised from.
Six at the top closes Kun, the upper trigram of Earth, at its highest place, with no line above it to answer to, and the image of collapse is deliberate rather than accidental, a peace that has run its full course and begun to revert toward the very undifferentiated ground the Judgment's great coming and small going first departed from. Legge's caution against using the army marks this collapse as internal exhaustion rather than external attack, a condition no show of force can reverse.
Set against the whole arc of Peace, from grass roots rising together to a sovereign's humble marriage, the sixth line is the hexagram's honest acknowledgment that no harmony, however well built, escapes eventual decline, and its counsel, order what remains within one's own walls rather than reaching for what is already lost, is offered without pretending the regret named can be entirely avoided.