In previous eras, opera and ballet were more intimately linked than they
are today. That is why the Palais Garnier in Paris has since 1875 been
home to both the Paris Opera and the Paris Opera Ballet — although most
operas are now performed in the Opera Bastille.

The Paris Ballet also has an associated school, the École de Danse de
l’Opéra de Paris, which this year celebrates its 300th year. In the early
days the dancers were male, with females entering into the mix in the late
17th and 18th centuries. The vision we have today of thin young females
dancing around in tutus was a creation of 19th century ballet

The dancers at the school are referred to as "the little rats" because
they scurry hither and thither among various practice rooms at the
Garnier in a very intense fashion — the school is extremely competitive.