While the Communist Party disavows the revolution’s 10 years of turmoil, it also bans free public debate about it. Instead it seeks to uphold its own judgment, from 1981, that Mao made “gross mistakes” in the Cultural Revolution, but that “his merits are primary and his errors secondary.”

Yet “the sky is high and the emperor far away,” runs a popular saying. Shantou, a fishing port formerly known as Swatow that is now a manufacturing hub of 13 million people, lies more than 1,100 miles south of the political capital in Beijing.

Until this year, that distance seemed to offer protection. Thousands of Chinese came to learn, to remember and to publicly mourn the victims, the only significant spot in the country where they could do so.

“We thought, as the country became more open and moved forward, the museum would improve,” said Mr. Peng, a sinewy man with a square jaw and bottlebrush gray hair, in an August interview in downtown Shantou’s Longhu district. “Spring would come. But we didn’t know that spring didn’t come, winter did.”

Dressed in a white singlet, blue-and-white pajama pants and brown plastic sandals, Mr. Peng said he believed that the order to cover up the museum was not local, but had come from “higher up.” He declined to discuss the matter further.

Government offices in Shantou were called for comment, but either the calls were not picked up, or those answering hung up when the subject was mentioned. Associates of Mr. Peng declined to answer questions, saying it was not convenient.