As pointed out in the comments here, Chinese government censors celebrated the twentieth anniversary of the Tiananmen Massacre by shutting down a bunch of the Internet.

Chinese services are facing so much pressure from the government to keep their users from talking about that bloody day, they are just shutting down comment boards, or claiming their services are closed for unspecified upgrades. For instance, FanFou.com, a popular Twitter-like service, shut its doors for the week, and says it will re-open on June 6.

Meanwhile, the so-called Great Firewall of China is blocking Twitter, human rights groups’ websites and blogging services hosted outside of China. Despite that censorship, the country is still very interested in the events of 20 years ago, when the government crushed an unprecedented pro-democracy protest in Beijing by unleashing the army on unarmed students. [Rebecca MacKinnon, the co-founder of Global Voices], the former Beijing Bureau Chief for CNN, noted that the top three hot queries on Google.cn were about the anniversary, despite Google’s willing censorship of search results. But Google does better than the Chinese-owned Baidu search engine, which reports no results for an image search for “Tiananmen Square.” Baidu’s blogging service also searches draft posts for keywords, and forbids publication of posts with controversial terms.

What's more, authorities put Tiananmen Square on a virtual lockdown. The Los Angeles Times has an interesting report of the day's events (or lack-thereof):

On this day, there are commemorative ceremonies all around the world - in Washington, London, Hong Kong, Los Angeles. Almost everywhere, it would seem, but here, where it happened.

Dissidents around China have been put under house arrest to prevent any attempt to enter the square. The foreign media have been barred for the day. The entire 10 acres are fenced off with police barricades. White tents like the ones used for the happier occasion of last summer's Olympic Games are outfitted with metal detectors. The authorities look not just for weapons, but also for papers and scarves that might be unfurled into a banner. Some visitors are asked to show their passports; those who have Chinese "J" visas (the letter indicating the holder is a journalist) are turned away.

Also, Slog commenter blip suggests the Frontline documentary The Tank Man, which you can stream here.

Via Wired.com and Latimes.com.