President Donald Trump took to Twitter Wednesday and Thursday to share updates about his visit to China — despite the communist country’s ban on Western social media platforms.

What is the Great Firewall?

The Chinese government has implemented a complex system to censor the internet. According to Reuters, the system, known as the Great Firewall, blocks those inside China from accessing websites like Facebook and Twitter. It does permit access to Chinese social media platforms like Weibo.

CNN noted that Chinese state media sometimes use platforms like Facebook, YouTube, and Twitter to share propaganda around the world.

What did Trump say?

The president, a prolific Twitter user, posted a series of Tweets while visiting China — an action forbidden to residents of the country.

He thanked Chinese President Xi Jinping and his wife, Peng Liyuan, for hosting him and first lady Melania Trump.

He posted another tweet warning North Korea not to threaten the United States. North Korea also blocks its citizens from visiting Western websites.

Trump also posted pictures from his visit to China on Instagram — another banned platform.

#PresidentTrump and #FirstLady Melania are welcomed upon their welcome to the #GreatHall of the People, this morning in #Beijing, #China, by #Chinese #President #XiJinping and First Lady #PengLiyuan. #POTUSinAsia #USA #China

A post shared by President Donald J. Trump (@realdonaldtrump) on Nov 8, 2017 at 9:56pm PST

How did he do it?

According to Reuters, it is unclear how Trump managed to bypass the Great Firewall.

Foreigners visiting China sometimes use virtual private networks to access the external internet. Others use a data-roaming service.

“The president will tweet whatever he wants,” an unnamed White House official told Reuters. “That’s his way of communicating directly with the American people. Why not?”