These three loops cannot be taken apart, but if you remove any one of them the other two will be disconnected. When any two loops are pulled apart, it’s clear that the other loop is the only thing keeping them together. These are called Borromean rings.

The name of Borromean rings comes from a famous family of Italian princes from the Renaissance era, the Borromeans, who adopted the rings as their heraldic symbol. They were carved into the stones of their castles, on one of the Borromean Islands in the Lago Maggiore (Isola Bella), in northern Italy.
This link can also be found on carved stones from around the 9th century, on Gotland, an island in the Baltic Sea off the south-eastern coast of Sweden. It is believed that they correspond to legends derived from Norse mythology. Besides, peoples from northern Scandinavia call a representation of the Borromean rings “Odin’s triangle”, or Valknut, “knot of the killed one”. The symbol was also carved into the frame of beds used during funerals at sea.

Gif: Matthen