Paris, which is itself a département, and the three surrounding départements, are governed by a single préfecture for law enforcement and security purposes, which is the préfecture de police. The préfet de police
has the power of law enforcement for Paris, which is a power of the mayor for the other French cities and towns.
Until 1977, Paris had indeed no mayor and was mostly ruled by the préfet de police
(a situation inherited from the Paris Commune, 1871). However, the powers of the mayor of Paris were increased at the expense of those of the Préfet de Police in 2002, notably for traffic and parking decisions (the préfet retains the responsibility on main thoroughfares such as the Champs-Élysées avenue, and on any street during the organization of demonstrations).