Original: In 1665, London was swept by a visitation of the plague, and then, in 1666, the capital was swept by the Great Fire, which raged for 5 days, destroying approximately 15,000 buildings.
Simplified: In 1665, London was hit with the plague, and then, in 1666, the capital was burned for 5 days by the Great Fire, destroying around 15,000 buildings.