Millions of these believers stubbornly resist government control. In some parts of China, the Catholic populations of entire counties attend underground churches, and the party-controlled churches stand almost empty, their clergy ignored.

All of this could change under the rapprochement between the Vatican and Beijing.

Several underground bishops in China, including two popular bishops in staunchly Catholic parts of the country, are expected to step down to make way for the bishops appointed by Beijing over the past decade whom the pope has agreed to recognize. In exchange, the pope is gaining some role in the appointment of new bishops. There are about 100 bishops and prelates in China, including underground and approved, and a dozen vacant positions.

Exactly how this will work is unclear. Both sides have described the agreement signed on Saturday as preliminary, and neither has released details. But some informal veto system seems likely. The Vatican could reject candidates suggested by the Chinese authorities, although mainly through quiet consultation rather than formal voting.

In the long run, diplomatic ties could be restored between Beijing and the Vatican.

Some Chinese Catholics see this as helping a church that has been unable to respond to changing times. China is rapidly urbanizing, for example, but many rural Catholics find little outreach when they migrate to take jobs in the cities. A unified church could address that.