pàntú / yǔ / dírén / lǐgōuwàilián / cái / shǐ / fángyùgōngshì / bèi / qīngyì / gōngpò

叛徒与敌人里勾外连，才使防御工事被轻易攻破。

The traitor collaborated with the enemy from within, which made the fortifications easily breached.