When the workers opened the wall of our house, something fell on the floor. It was small and black and very dirty. My father picked it up and washed it. It was a coin. We could not read the writing on it, so we took it to the museum in the town. The woman there put it under a light and looked at it for two minutes. "It is about four hundred years old," she said. "It is not valuable. There are thousands of these." My father was disappointed. "But it is interesting," she continued. "People put coins inside walls for luck. Somebody built your house and hoped it would stand." "Did it work?" I asked. She smiled. "Your house is still standing." We did not sell the coin. My father put it back inside the new wall before the workers closed it. "For the next four hundred years," he said. Nobody in my family knows exactly where it is now, and that is the point.