Today, the limits of the city of Paris which is at the same time the département of Paris (n° 75) coincide with the expressway Boulevard Périphérique (“le Périph’” or “BP”), a 35km-long dual carriageway with the particular rule that entrants have priority over those already on the expressway. The speed limit is 70km/h but most of the time traffic jams don’t allow for that speed anyway. The Périphérique intérieur runs clockwise, the Périphérique extérieur counter-clockwise.
The strip between the boulevards des Maréchaux (“les Maréchaux”) and the Périph’ is occupied by social housing, schools, and sports equipment.
There are three “extensions” to the surface of the city of Paris that lie outside of this limit: the Bois de Boulogne park to the west, the Bois de Vincennes park to the east, and the Paris heliport in the southwest near the Seine river, belonging to the 15tharrondissement.
The final city wall that was an actual wall was built between 1841 and 1844 on the orders of Adolphe Thiers, President of the Council, a position that corresponded to that of Prime Minister. It ran around the entire city, a space of almost 80km² and followed the boulevards des Maréchaux, a 33,7km-long ring road named after Marshals of the First French Empire that circles Paris and can today be traced by the PC (Petite Ceinture) buses (west) and the tram lines T3A (south and east) and T3B (east and north).
It was destroyed between 1919 and 1929, and only very few short sections remain, such as Bastion 44 in the rue du Bastion in the 17tharrondissement, the Poterne des Peupliers (a postern) in the 13tharrondissement or Bastion 1 at Porte de Bercy in the 12tharrondissement, in the middle of the Bercy interchange.