The Trojan asteroids that circle in Jupiter’s orbit and give the asteroid belt a triangular shape cluster around Lagrangian points as shown here:

(text below by astronomer Ole Olson)
Trojan Asteroids at Jupiters Lagrange Points

With Lagrangian points other stable patterns are possible, and so happen. A stable 3:2 resonance pattern of asteroids whose motion gets confined to a basically triangular shape by the combined pull of Jupiter and the Sun. Around Jupiter this group of asteroids is called the Hilda Family, and their route forms a triangle with its three points at the two Lagrange points and at the point on Jupiter’s orbit directly opposite it from the Sun.
http://www.exploremars.org/trojan-asteroids-around-jupiter-explained