The first line of the Paris Metro, which was only the fifth subway in the world at the time, opens for operation during the Exposition Universelle. And one hundred and fifteen years later it is the second busiest subway system in Europe (after Moscow).
While not critical from the perspective of moving goods in the supply chain, it is important to remember that the information, finance, and physical supply chains all run on people, who have to get to work, get around, and get things done. Something tough to do in a big, dense, city with well over 10 million people.