In 1858, Queen Victoria sent a telegraph to U.S. President Buchanan, via the first undersea cable.

The cable worked for just a few weeks, but it launched an international cable network that still dominates global communication.

We think we live in a wireless world. But it’s just the short hop from our phones and wifi to a receiving antenna. Nearly everything after that is transmitted by cable, on land and undersea.

Undersea cables made of copper served the world for more than a hundred years. Then, in 1988, the first fiber-optic cable was laid.

They’re made of strands of ultrapure glass, no thicker than a human hair. Hundreds of strands are bundled together and protected by braided metal and nylon, jacketed in plastic.

At one end, electrical signals are converted to light by a laser, then shot down the fiber-optic cable, sometimes more than a thousand miles, between countries and continents.

In the shallows, they’re buried in trenches to protect them. In deep water, they’re simply laid on the seabed, which is less expensive, but exposes them to harm.

There are now thousands of subsea fiber-optic cables, stretching almost 1 million total miles, transmitting 95% of international internet and voice traffic. And more cables are being laid each year.

So next time you make an international call, pause for a moment to imagine your voice rocketing along at the speed of light, under the sea.