Chemin de fer de Petite Ceinture
Paris's Chemin de fer de Petite Ceinture (French pronunciation: [ʃəmɛ̃ də fɛʁ də pətit sɛ̃tyʁ], 'small(er) belt railway'), also colloquially known as La Petite Ceinture, is a circular railway built as a means to supply the city's fortification walls, and as a means of transporting merchandise and passengers between the major rail-company stations in Paris. Beginning as two distinct 'Ceinture Syndicate' freight and 'Paris-Auteuil' passenger lines from 1851, they formed an arc that surrounded the northern two thirds of Paris, an arc that would become a full circle of rail around the capital when its third Ceinture Rive Gauche section was built in 1867.
Source: Wikipedia — Chemin de fer de Petite Ceinture (CC BY-SA 4.0)