Given the task definition and input, reply with output. Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Almost nothing is left of the Bastille except some remains of its stone foundation that were relocated to the side of the Boulevard Henri IV. Historians were critical of the Bastille in the early 19th century, and believe the fortress to have been a relatively well-administered institution, but deeply implicated in the system of French policing and political control during the 18th century.
Question: What material was used for Bastille?
stone