众zhòng志zhì成chéng城chéng

Literal: the will of the many makes a city wall
Figurative: Many people united like a wall nothing can breach; more solemn than 齐心协力, it is usually said in the face of a disaster or a shared threat.

Where does 众志成城 come from?

It comes from the 《国语》. King Jing of Zhou had a great bell cast even though his advisers, among them the court musician Zhou Jiu, urged him not to. When the bell was finished, the musicians told the king it sounded harmonious, and he mentioned this to Zhou Jiu. Zhou Jiu replied that he could not tell whether it was, since the project had emptied the treasury and worn out the people, and he quoted a saying: "Many hearts make a city wall; many mouths melt metal." From it, with 志 in place of 心, came the idiom. Today it is heard in calls for unity in the face of floods, earthquakes or epidemics.

Source (出处): 《国语·周语下》

How is 众志成城 used? Two examples

台tái风fēng来lái袭xí，全quán市shì众zhòng志zhì成chéng城chéng，一yī夜yè之zhī间jiān转zhuǎn移yí了le上shàng万wàn名míng群qún众zhòng。
When the typhoon struck, the whole city stood together and evacuated more than ten thousand people overnight.
公gōng司sī最zuì难nán的de那nà一yī年nián，大dà家jiā众zhòng志zhì成chéng城chéng，没méi有yǒu一yī个gè人rén离lí开kāi。
In the company's hardest year, everyone closed ranks against the crisis and not a single person left.

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