It is a high-tech high-security fortress in London.

At $1 billion, the new U.S. embassy in the UK is the most expensive ever. The walls are blast-resistant. The glass is shatter-proof. It is diplomacy in the age of terror.

“The world has changed and so this building meets all those challenges,” Woody Johnson, U.S. Ambassador to the UK, told Fox News.

One important security feature, and an appropriate one for an embassy in the land of castles: A 100-foot-wide “moat,” at least one that protects one side of the building. Staffers like to call it a “pond.”

It was the exposed nature of the old U.S. embassy that helped push this move. Five often deadly terror strikes in the UK this year underscored it.

“An urban environment like we’ve seen in London with attacks,” embassy architect James Timberlake told Fox News, “are unknown and can happen any time.”

The new embassy, just south of the Thames River, is more remote.

But it’s not without risk. Suspicious vehicles near the site triggered controlled detonations earlier this year.

“You have to take the rough with the smooth,” said Ravi Govindia, leader of London borough of Wandsworth. “Of course, there will be concerns and disruptions.”

1,000 embassy staffers will be housed in a safe and open environment. The sale of the old embassy and another property paid for the new one.

The new embassy opens to the public January 16. According to Ambassador Johnson, the embassy will be dedicated by President Trump during a visit scheduled for early next year.