As the Olympics nears, Paris puts 75,000 troops on the streets : A scrum of disappointed tourists stared, wistfully, through the maze of metal fences lining the River Seine. Ahead of them, Notre Dame cathedral and other Parisian treasures lay, tantalisingly, out of reach. “We don’t have a code,” said a woman from Mexico, watching others – armed with the requisite QR security code – pass, with an approving beep, through a police checkpoint. Further downstream, beside the Eiffel Tower, a weary couple trailing large suitcases performed a slow U-turn on a crowded pavement. “Closed. You’ll have to walk around,” a French gendarme had just told them, gesturing towards the south. As Paris prepares to unveil its unique Olympic opening ceremony – a river-based extravaganza that will see athletes on burnished barges being paraded through the heart of the French capital on Friday evening – the country’s police and armed forces are laying the finishing touches to an equally unprecedented security