The Arc de Triomphe was built by Napoleon at the end of the Champs Elysees to commemorate his war victories.  During the Second Empire, the Baron de Haussmann made it the focal point of his New Paris, the radial point of all of his grand boulevards that stitched the city together.  It is an elegant testimony to what grand-scale planning can accomplish, even if it did destroy the medieval city in the process.