Detailed Instructions: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Q: What was the catalyst for the dissolution of the Vestals?, Context: Augustus' religious reformations raised the funding and public profile of the Vestals. They were given high-status seating at games and theatres. The emperor Claudius appointed them as priestesses to the cult of the deified Livia, wife of Augustus. They seem to have retained their religious and social distinctions well into the 4th century, after political power within the Empire had shifted to the Christians. When the Christian emperor Gratian refused the office of pontifex maximus, he took steps toward the dissolution of the order. His successor Theodosius I extinguished Vesta's sacred fire and vacated her temple.
A:
When the Christian emperor Gratian refused the office of pontifex maximus