tā / men / fèng / mìng / shù / shǒu / zhè / zuò / gǔ / chéng / zhí / dào / xīn / de / bù / duì / qián / lái / jiē / tì

他们奉命戍守这座古城，直到新的部队前来接替。

They were ordered to guard the ancient city until a new unit arrived to take over.