The Circle of SpongeBob Statues are a group of giant stone statues of SpongeBob SquarePants. They were built in the episode SpongeHenge which is so far their only appearance.
The reason why they were built is that SpongeBob needed them to escape from the jellyfish that wouldn't leave him alone. They wouldn't leave him alone because a strong wind was blowing, and it made a tune when it blew through SpongeBob's holes that jellyfish seem to love. The jellyfish wouldn't leave SpongeBob alone, thus preventing him from going about his day. He tried to flee, but the jellyfish kept on following him, forcing SpongeBob to take refuge in a cave were the wind didn't blow. SpongeBob decide just to wait in the cave until the wind stopped blowing, but it never seemed to stop. He eventually made a stone carving of himself out of insanity. When SpongeBob blew into one of its hole, he discovered that it made a tune. When he tried to use it to distract the jellyfish, it only made a shrill noise that made them angry. So SpongeBob concluded that he needed to make another stone carving of himself in a different size, but he didn't know how big to make them, so he made a bunch of them. He ended up making a bunch of large ones and put them in a circle. Their tune was just right to distract the jellyfish, allowing SpongeBob to escape.
3,000 years later, a race of aliens is seen, and the statues are now a tourist attraction. The aliens don't know who built them or why they were built, only that their tune causes the annual migration of jellyfish. You can hear SpongeBob's laugh at the closing scene.