(87) Sylvia was discovered in 1866 by N.R. Pogson, a British astronomer located in Madras, India. This main-belt asteroid is large with a diameter of ~150 km. That's all we knew until recently.
In 2005, we discovered two moons around the asteroid that we called Romulus and Remus, sons of the Rhea Sylvia and founder of Rome. Both moons are very small with a diameter estimated to ~7 and ~20 km. The primary is irregular with a diameter of 193 x 129 x 124 km. Both moons orbit around the primary describing a coplanar and almost circular orbit.
From a long term study of their orbit we concluded that the primary is possibly differentiated, made of a dense core of ice. How the moons have formed is still unclear. They could be the product of a catastrophic disruption of a large asteroid early in the history of the solar system. (87) Sylvia is the first known triple asteroid. Today we know five of them in the asteroid main-belt.