This triumphant arch was completely walled off by a graffitied fence. It is the Porta Sempione or Arch of Peace. Rick Steves
describes it as the "Arco della Pace" and says "They built the arch facing Paris to welcome Napoleon's rule, because locals believed he would bring with him the ideals of the French Revolution. When they learned he was just another megalomaniac, they turned the horses around, their tails facing France." You can't see the horses in this picture. I find it somewhat ironic that the arch of peace doesn't allow you to walk under it.