Arthropleura was a seven-foot millipede that lived in the Carboniferous Period. The Carboniferous Period also had a lot of other giant arthropods. The name is pronounced arthro-PLEW-ruh.
Arthropleura could literally stand up, half of it pointing up in the air, and half of it on the bottom holding it up. Even though Arthropleura ate ferns and other plants, it did have strong mandibles that could really injure someone.
The reason the giant arthropods were alive only in the Carboniferous Period is because the whole entire world was either ocean or a swamp. Swamps are usually known to have millions of plants, so imagine if the whole world was covered in a swamp. Then there'd be a lot of oxygen, because plants make oxygen. An arthropod would have trouble getting the oxygen to all its different parts if there wasn't enough oxygen, so all the oxygen would allow the arthropods to get very, very big.