This is an old arch bridge, that can but should be not used for carrying heavy loads across, because it is so old. these were common in Rome and Asia which were mainly used for walking, and of course for Rome, marching of the roman army. In today's time we use arch bridges for our highways and streets, but they can be easy to fall through if not with the right material and structure placement.
Today in class we watched "To Engineering is human'. This was a short film about technological and engineering failures, but how these failures have improved our society in the long run. One of the structural failures i saw was at the beginning, the space shuttle that caught on fire, also there was the arena that the roof caved in because of snow and sleet, and the structure could not hold the weight of all of that. Without the right materials, and the known amount of stress put on the materials, every building would be collapsing, because we could not know, if the structure would support itself, and if it couldn't what would we need to make it do that job. As the man said in the video, Failure is necessary for success, but in the same way success is necessary for failure. If we don't fail in these engineering projects, then we could not evolve to find the best solution to these problems. without the solutions, there would still be a great amount of failure, but the success would be minimal. Engineers take safety in account first, when they build the structure, so they know no one will get hurt. they can experience this failure through minimal tests, scale models, and making the building or structure, and not letting anyone use it.