The Parisian Rail System is a comprehensive network of public transportation that includes the METRO, which is the most popular form of transportation in the city. The METRO consists of 16 lines that span across the city and its suburbs, providing easy access to all areas of the city. It is one of the oldest and most extensive METRO systems in the world, having been in operation since 1900. The METRO is an efficient and affordable way to get around the city, making it a popular choice for both locals and tourists alike.