In fact, those shields were placed by ARATAO no Akamaro and IMIBE no Kobito before the battle at Mt. Nara, and the real force for guarding the city was very poor and undermanned.
その楯は、乃楽山の戦いの前に荒田尾赤麻呂と忌部子人が並べたもので、京を守る兵力は少なかった。